Magnetic recording medium and cartridge

ABSTRACT

A magnetic recording medium is a magnetic recording medium having a tape shape and includes a substrate, an underlayer provided on the substrate, and a magnetic layer provided on the underlayer. The magnetic layer has a surface having an uneven shape, a height range ΔH obtained from statistical information of a height of the uneven shape is in a range of 4.00 nm ≤ ΔH ≤ 10.00 nm, and a gradient range ΔA obtained from statistical information of a gradient of the uneven shape is in a range of 2.50 degrees ≤ ΔA.

TECHNICAL FIELD

The present disclosure relates to a magnetic recording medium and acartridge.

BACKGROUND ART

Tape-shaped magnetic recording media have been widely used to storeelectronic data. In a tape-shaped magnetic recording medium, it isdesired to reduce the height of irregularities on the surface of amagnetic layer and flatten the surface of the magnetic layer in order toobtain satisfactory recording/reproducing characteristics(electromagnetic conversion characteristics) (see, for example, PTL 1).

CITATION LIST Patent Literature PTL 1

JP 2006-65953 A

SUMMARY Technical Problem

However, a reduction in the height of irregularities on the surface ofthe magnetic layer results in running instability, such as an increasein friction, as an adverse effect.

An object of the present disclosure is to provide a magnetic recordingmedium capable of achieving both excellent recording/reproducingcharacteristics and excellent running stability and a cartridgeincluding the magnetic recording medium.

Solution to Problem

In order to solve the problems described above, a first disclosure is amagnetic recording medium with a tape shape including

-   a substrate,-   an underlayer provided on the substrate, and-   a magnetic layer provided on the underlayer,-   wherein the magnetic layer has a surface having an uneven shape,-   a height range ΔH obtained from statistical information of a height    of the uneven shape is in a range of 4.00 nm ≤ ΔH ≤ 10.00 nm, and-   a gradient range ΔA obtained from statistical information of a    gradient of the uneven shape is in a range of 2.50 degrees ≤ ΔA.

A second disclosure is a cartridge including the magnetic recordingmedium according to the first disclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded perspective view illustrating an example of aconfiguration of a cartridge according to an embodiment of the presentdisclosure.

FIG. 2 is a block diagram illustrating an example of a configuration ofa cartridge memory.

FIG. 3 is a cross-sectional view illustrating an example of aconfiguration of a magnetic tape.

FIG. 4 is a schematic diagram illustrating an example of a layout ofdata bands and servo bands.

FIG. 5 is an enlarged view illustrating an example of a configuration ofa data band.

FIG. 6 is an enlarged view illustrating an example of a configuration ofa servo band.

FIGS. 7A and 7B are diagrams illustrating an example of a TEM photographof a magnetic layer.

FIG. 8A is a diagram illustrating an example of a two-dimensionalsurface profile image after a filter action. FIG. 8B is a diagramillustrating an example of a numerical data matrix of a height ζ(L,W).

FIG. 9 is a diagram illustrating an example of a numerical data matrixof a relative height Z(L,W).

FIG. 10 is a diagram illustrating a method of calculating gradientsG_(L)(L,W) and G_(W)(L,W) at each point (L,W).

FIG. 11A is a diagram illustrating an example of a numerical data matrixof a gradient G_(L)(L,W). FIG. 11B is a diagram illustrating an exampleof a numerical data matrix of a gradient G_(W)(L,W).

FIG. 12A is a diagram illustrating a method of calculating a gradientG_(L)(L,W). FIG. 12B is a diagram illustrating a method of calculating agradient Gw(L,W).

FIG. 13 is a diagram illustrating statistical processing of data havinga relative height Z(L,W) and a gradient G_(L)(L,W).

FIG. 14 is a diagram illustrating statistical processing of data havinga relative height Z(L,W) and a gradient Gw(L,W).

FIG. 15 is a diagram illustrating statistical processing of data havinga relative height Z(L,W), a gradient G_(L)(L,W), and a gradient Gw(L,W).

FIG. 16 is a diagram illustrating a procedure of creating a distributionmap from a numerical data matrix of the number of pieces of data M(H,A).

FIG. 17 is a diagram illustrating a method of calculating a height rangeΔH.

FIG. 18 is a diagram illustrating a method of calculating a height rangeΔH.

FIG. 19 is a diagram illustrating a method of calculating a gradientrange ΔA.

FIG. 20 is a diagram illustrating a method of calculating a gradientrange ΔA.

FIGS. 21A and 21B are diagrams illustrating a method of measuring theamount of oozing of a lubricant.

] FIGS. 22A and 22B are schematic diagrams illustrating a method ofmeasuring a friction coefficient between a magnetic surface and amagnetic head.

FIG. 23 is an exploded perspective view illustrating an example of aconfiguration of a cartridge according to a modification example of theembodiment of the present disclosure.

FIG. 24 is a graph illustrating a relationship between a height range ΔHand a gradient range ΔA.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present disclosure will be described in thefollowing order.

-   1 Configuration of cartridge-   2 Configuration of cartridge memory-   3 Configuration of magnetic tape-   4 Method of manufacturing magnetic tape-   5 Effects-   6 Modification Examples

1 Configuration of Cartridge

FIG. 1 is an exploded perspective view illustrating an example of aconfiguration of a cartridge 10. The cartridge 10 includes a reel 13 onwhich a tape-shaped magnetic recording medium (hereinafter referred toas a “magnetic tape”) MT is wound, a reel lock 14 and a reel spring 15for locking the rotation of the reel 13, a spider 16 for releasing alocked state of the reel 13, a slide door 17 that opens and closes atape drawing port 12C provided in a cartridge case 12 across a lowershell 12A and an upper shell 12B, a door spring 18 that biases the slidedoor 17 against a closed position of the tape drawing port 12C, a writeprotect 19 for preventing erroneous erasure, and a cartridge memory 11inside the cartridge case 12 constituted by the lower shell 12A and theupper shell 12B. The reel 13 has a substantially disk shape having anopening in the center part, and is constituted by a reel hub 13A made ofa hard material such as a plastic and a flange 13B. A leader pin 20 isprovided at one end of the magnetic tape MT.

The cartridge 10 may be a magnetic tape cartridge based on a lineartape-open (LTO) standard or may be a magnetic tape cartridge based on astandard different from the LTO standard.

The cartridge memory 11 is provided in the vicinity of one corner of thecartridge 10. When the cartridge 10 is loaded in a recording/reproducingdevice, the cartridge memory 11 faces a reader/writer of therecording/reproducing device. The cartridge memory 11 communicates witha recording/reproducing device, specifically, a reader/writer based on awireless communication standard according to the LTO standard.

2 Configuration of Cartridge Memory

FIG. 2 is a block diagram illustrating an example of a configuration ofthe cartridge memory 11. The cartridge memory 11 includes an antennacoil (communication unit) 31 that communicates with a reader/writeraccording to a specified communication standard, a rectification andpower circuit 32 that generates power by generating and rectifying powerfrom radio waves received by the antenna coil 31 using an inducedelectromotive force, a clock circuit 33 that similarly generates a clockusing an induced electromotive force from radio waves received by theantenna coil 31, a detection and modulation circuit 34 that detectsradio waves received by the antenna coil 31 and modulates a signaltransmitted by the antenna coil 31, a controller (control unit) 35 whichis constituted by a logic circuit or the like for discriminating acommand and data from a digital signal extracted from the detection andmodulation circuit 34 and processing the command and data, and a memory(storage unit) 36 that stores information. In addition, the cartridgememory 11 includes a capacitor 37 which is connected to the antenna coil31 in parallel, and a resonance circuit is constituted by the antennacoil 31 and the capacitor 37.

The memory 36 stores information and the like related to the cartridge10. The memory 36 is a non-volatile memory (NVM). A storage capacity ofthe memory 36 is preferably approximately 32 KB or more.

The memory 36 includes a first storage region 36A and a second storageregion 36B. The first storage region 36A is, for example, a regioncorresponding to a storage region of an LTO standard cartridge memory(hereinafter referred to as a “cartridge memory of the related art”) ofLTO8 or earlier and storing information based on the LTO standard ofLTO8 or earlier. The information based on the LTO standard of LTO8 orearlier is, for example, manufacture information of the cartridge 10(for example, an inherent number or the like of the cartridge 10), a usehistory (for example, a thread count or the like), and the like.

The second storage region 36B is equivalent to an extended storageregion with respect to the storage region of the cartridge memory of therelated art. The second storage region 36B is a region for storingadditional information. Here, the additional information is, forexample, information related to the cartridge 10 which is not specifiedby an LTO standard of LTO8 or earlier. Examples of the additionalinformation include tension adjustment information, management recorddata, index information, thumbnail information of a moving image storedin the magnetic tape MT, and the like, but are not limited to thesetypes of data. The tension adjustment information is information foradjusting tension applied in the longitudinal direction of the magnetictape MT. The tension adjustment information includes a distance betweenadjacent servo bands (a distance between servo patterns recorded in theadjacent servo bands) during data recording in the magnetic tape MT. Thedistance between the adjacent servo bands is an example of width-relatedinformation related to the width of the magnetic tape MT. In thefollowing description, information stored in the first storage region36A may be referred to as “first information”, and information stored inthe second storage region 36B may be referred to as “secondinformation”.

The memory 36 may include a plurality of banks. In this case, the firststorage region 36A may be constituted by some of the plurality of banks,and the second storage region 36B may be constituted by the remainingbanks.

The antenna coil 31 induces an induced voltage by electromagneticinduction. The controller 35 communicates with the recording/reproducingdevice according to a specified communication standard through theantenna coil 31. Specifically, the controller performs, for example,mutual authentication, transmission and reception of commands, dataexchange, and the like.

The controller 35 stores information received from therecording/reproducing device through the antenna coil 31 in the memory36. For example, tension adjustment information received from therecording/reproducing device through the antenna coil 31 is stored inthe second storage region 36B of the memory 36. The controller 35 readsinformation from the memory 36 in response to a request of therecording/reproducing device and transmits the information to therecording/reproducing device through the antenna coil 31. For example,the controller 35 reads tension adjustment information from the secondstorage region 36B of the memory 36 in response to a request of therecording/reproducing device and transmits the tension adjustmentinformation to the recording/reproducing device through the antenna coil31.

3 Configuration of Magnetic Tape

FIG. 3 is a cross-sectional view illustrating an example of aconfiguration of the magnetic tape MT. The magnetic tape MT includes along substrate 41, an underlayer 42 provided on one main surface (firstmain surface) of the substrate 41, a magnetic layer 43 provided on theunderlayer 42, and a back layer 44 provided on the other main surface(second main surface) of the substrate 41. Here, the underlayer 42 andthe back layer 44 may be provided as necessary or may not be provided.The magnetic tape MT may be a perpendicular recording type magneticrecording medium, or may be a longitudinal recording type magneticrecording medium.

The magnetic tape MT may be based on an LTO standard or may be based ona standard different from the LTO standard. The width of the magnetictape MT may be ½ inch or may be larger than ½ inch. In a case where themagnetic tape MT is based on the LTO standard, the width of the magnetictape MT is ½ inch. The magnetic tape MT may have a configuration inwhich the width of the magnetic tape MT is kept constant orsubstantially constant by adjusting tension applied in the longitudinaldirection of the magnetic tape MT during running by therecording/reproducing device (drive).

The magnetic tape MT has a long shape and runs in the longitudinaldirection at the time of recording/reproducing. Note that the surface ofthe magnetic layer 43 is a surface on which a magnetic head included inthe recording/reproducing device runs. The magnetic tape MT ispreferably used in a recording/reproducing device including a ring-typehead as a recording head. The magnetic tape MT is preferably used in arecording/reproducing device configured to be able to record data with adata track width of 1500 nm or less or 1000 nm or less.

Substrate

The substrate 41 is a non-magnetic support that supports the underlayer42 and the magnetic layer 43. The substrate 41 has a long film shape. Anupper limit value of an average thickness of the substrate 41 ispreferably 4.4 µm or less, more preferably 3.8 µm or less, and stillmore preferably 3.4 µm or less. When the upper limit value of theaverage thickness of the substrate 41 is 4.4 µm or less, a recordingcapacity capable of being recorded in one data cartridge can beincreased more than in a general magnetic tape. A lower limit value ofthe average thickness of the substrate 41 is preferably 3 µm or more,and more preferably 3.2 µm or more. When the lower limit value of theaverage thickness of the substrate 41 is 3 µm or more, it is possible tominimize a decrease in the strength of the substrate 41.

The average thickness of the substrate 41 is obtained as follows. First,a magnetic tape MT is prepared and cut to a length of 250 mm to preparea sample. Subsequently, the layers (that is, the underlayer 42, themagnetic layer 43 and the back layer 44) of the sample other than thesubstrate 41 are removed with a solvent such as methyl ethyl ketone(MEK) or diluted hydrochloric acid. Next, the thickness of the sample(the substrate 41) is measured at positions of 5 or more points using aLaser Hologage (LGH-110C) (commercially available from Mitutoyo) as ameasurement device, and the average thickness of the substrate 41 iscalculated by simply averaging (taking an arithmetic mean of) thesemeasured values. Here, the measurement positions are randomly selectedfrom the sample.

The substrate 41 preferably contains polyester. When the substrate 41contains polyester, it is possible to reduce the Young’s modulus of thesubstrate 41 in the longitudinal direction. Therefore, when the tensionof the magnetic tape MT in the longitudinal direction during running isadjusted by the recording/reproducing device, the width of the magnetictape MT can be kept constant or substantially constant.

The polyester includes, for example, at least one of polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), polybutyleneterephthalate (PBT), polybutylene naphthalate (PBN), polycyclohexylenedimethylene terephthalate (PCT), polyethylene-p-oxybenzoate (PEB) andpolyethylene bisphenoxycarboxylate. When the substrate 41 contains twoor more types of polyesters, these two or more types of polyesters maybe mixed, copolymerized, or laminated. At least one of the ends and sidechains of the polyester may be modified.

When polyester is incorporated into the substrate 41, this is confirmed,for example, as follows. First, in the same manner as in the method ofmeasuring an average thickness of the substrate 41, the layers of thesample other than the substrate 41 are removed. Next, an infraredabsorption spectrometry (IR) spectrum of the sample (the substrate 41)is acquired IR. Incorporation of the polyester into the substrate 41 canbe confirmed based on the IR spectrum.

In addition to the polyester, for example, the substrate 41 may furthercontain at least one of a polyamide, a polyimide and a polyamide-imide,or may further contain at least one of a polyamide, a polyimide, apolyamide-imide, polyolefins, cellulose derivatives, a vinyl resin, andother polymer resins. The polyamide may be an aromatic polyamide(aramid). The polyimide may be an aromatic polyimide. Thepolyamide-imide may be an aromatic polyamide-imide.

When the substrate 41 contains a polymer resin other than the polyester,the substrate 41 preferably contains polyester as a main component.Here, the main component is a component of which the content (massproportion) is the largest among the polymer resins contained in thesubstrate 41. When the substrate 41 contains a polymer resin other thanthe polyester, the polyester and the polymer resin other than thepolyester may be mixed or copolymerized.

The substrate 41 may be biaxially stretched in the longitudinaldirection and the width direction. The polymer resin contained in thesubstrate 41 is preferably oriented obliquely with respect to the widthdirection of the substrate 41.

Magnetic Layer

The magnetic layer 43 is a recording layer in which a signal is recordedby a magnetization pattern. The magnetic layer 43 may be a perpendicularrecording type recording layer or a longitudinal recording typerecording layer. The magnetic layer 43 contains, for example, a magneticpowder, a binding agent, and a lubricant. The magnetic layer 43 mayfurther contain, as necessary, at least one additive among an antistaticagent, an abrasive, a curing agent, an antirust agent, non-magneticreinforcing particles, and the like. The magnetic layer 43 has a surfacehaving an uneven shape. A plurality of concave portions (notillustrated) may be provided on the surface of the magnetic layer 43.

As illustrated in FIG. 4 , a plurality of servo bands SB and a pluralityof data bands DB may be provided on the magnetic layer 43 in advance.The plurality of servo bands SB are provided at equal intervals in thewidth direction of the magnetic tape MT. A data band DB is providedbetween adjacent servo bands SB. The servo bands SB are used to guide amagnetic head (specifically, servo read heads 56A and 56B) at the timeof data recording or data reproducing. In each servo band SB, a servopattern (servo signal) for controlling tracking of the magnetic head iswritten in advance. User data is recorded in the data band DB.

An upper limit value of a ratio Rs(= (S_(SB)/S) × 100) of a total areaS_(SB) of the plurality of servo bands SB with respect to an area S ofthe surface of the magnetic layer 43 is preferably 4.0% or less, morepreferably 3.0% or less, and still more preferably 2.0% or less from theviewpoint of securing a high recording capacity. On the other hand, alower limit value of the ratio Rs of the total area S_(SB) of theplurality of servo bands SB with respect to the area S of the surface ofthe magnetic layer 43 is preferably 0.8% or more from the viewpoint ofsecuring five or more servo bands SB.

The ratio R_(S) of the total area S_(SB) of the plurality of servo bandsSB with respect to the area S of the entire surface of the magneticlayer 43 is obtained as follows. The magnetic tape MT is developed usinga ferricolloid developer (commercially available from Sigma Hi-ChemicalInc., SigMarker Q), the developed magnetic tape MT is then observedunder an optical microscope, and the servo bandwidth W_(SB) and thenumber of servo bands SB are measured. Next, the ratio Rs is obtainedfrom the following formula. Ratio Rs[%] = (((servo bandwidth W_(SB)) ×(the number of servo bands SB))/(width of the magnetic tape MT)) × 100

The number of servo bands SB is, for example, 5+4n (where, n is aninteger of 0 or more) or more. The number of servo bands SB ispreferably 5 or more, and more preferably 9 or more. When the number ofservo bands SB is 5 or more, it is possible to minimize the influence onthe servo signal due to the change in the size of the magnetic tape MTin the width direction, and it is possible to secure stablerecording/reproducing characteristics with fewer off-track errors. Theupper limit value of the number of servo bands SB is not particularlylimited, and is, for example, 33 or less.

The number of servo bands SB is obtained in the same manner as in theabove method of calculating the ratio Rs.

In order to secure a high recording capacity, the upper limit value ofthe servo bandwidth W_(SB) is preferably 95 µm or less, more preferably60 µm or less, and still more preferably 30 µm or less. The lower limitvalue of the servo bandwidth W_(SB) is preferably 10 µm or more. It isdifficult to manufacture a magnetic head capable of reading a servosignal of the servo bandwidth W_(SB) of less than 10 µm.

The width of the servo bandwidth W_(SB) is obtained in the same manneras in the above method of calculating the ratio Rs.

As illustrated in FIG. 5 , the magnetic layer 43 is configured such thata plurality of data tracks Tk can be formed in the data band DB. Fromthe viewpoint of improving a track recording density and securing a highrecording capacity, the upper limit value of the data track width W ispreferably 2,000 nm or less, more preferably 1,500 nm or less, and stillmore preferably 1,000 nm or less. The lower limit value of the datatrack width W is preferably 20 nm or more in consideration of themagnetic particle size.

In order to secure a high recording capacity, the magnetic layer 43 hasa configuration in which data can be recorded so that the minimum valueL of the distance between magnetization reversals is preferably 48 nm orless, more preferably 44 nm or less, and still more preferably 40 nm orless. The lower limit value of the minimum value L of the distancebetween magnetization reversals is preferably 20 nm or more inconsideration of the magnetic particle size.

The magnetic layer 43 has a configuration in which data can be recordedso that the minimum value L of the distance between magnetizationreversals and the data track width W satisfy preferably W/L ≤ 35, morepreferably W/L ≤ 30, and still more preferably W/L ≤ 25. When theminimum value L of the distance between magnetization reversals is acertain value, and the minimum value L of the distance betweenmagnetization reversals and the track width W satisfy W/L > 35 (that is,when the track width W is large), since the track recording density doesnot increase, a sufficient recording capacity may not be secured. Inaddition, when the track width W is a certain value, and the minimumvalue L of the distance between magnetization reversals and the trackwidth W satisfy W/L > 35 (that is, when the minimum value L of thedistance between magnetization reversals is small), the bit lengthbecomes smaller, and the line recording density increases, butelectromagnetic conversion characteristics may significantly deterioratedue to the influence of the spacing loss. Therefore, in order to securethe recording capacity and minimize deterioration of electromagneticconversion characteristics, the W/L is preferably in a range of W/L ≤ 35as described above. The lower limit value of W/L is not particularlylimited, and is, for example, 1 ≤ W/L.

The data track width W is obtained as follows. The magnetic tape MT inwhich data is recorded on the entire surface is prepared, a datarecording pattern of the data band DB part of the magnetic layer 43 isobserved using a magnetic force microscope (MFM) to obtain an MFM image.As the MFM, Dimension 3100 (commercially available from DigitalInstruments) and its analysis software are used. The measurement regionof the MFM image is set to 10 µm × 10 µm, and the 10 µm × 10 µmmeasurement region is divided into 512 × 512 (= 262,144) measurementpoints. Three 10 µm × 10 µm measurement regions at different locationsare measured using the MFM, that is, three MFM images are obtained. Fromthe obtained three MFM images, using analysis software bundled inDimension 3100, the track width is measured at 10 locations, and anaverage value (simple average) is obtained. The average value is thedata track width W. Here, the measurement conditions of the MFM are asfollows: sweep rate: 1 Hz, chip used: MFMR-20, lift height: 20 nm, andcorrection: Flatten order 3.

The minimum value L of the distance between magnetization reversals isobtained as follows. The magnetic tape MT in which data is recorded onthe entire surface is prepared, a data recording pattern of the databand DB part of the magnetic layer 43 is observed using a magnetic forcemicroscope (MFM) to obtain an MFM image. As the MFM, Dimension 3100(commercially available from Digital Instruments) and its analysissoftware are used. The measurement region of the MFM image is set to 2µm × 2 µm, and the 2 µm × 2 µm measurement region is divided into 512 ×512 (= 262,144) measurement points. Three 2 µm × 2 µm measurementregions at different locations are measured using the MFM, that is,three MFM images are obtained. 50 inter-bit distances are measured fromthe two-dimensional unevenness chart of the recording pattern of theobtained MFM image. The inter-bit distance is measured using analysissoftware bundled in Dimension 3100. The value that is approximately thegreatest common divisor of the measured 50 inter-bit distances is theminimum value L of the distance between magnetization reversals. Here,the measurement conditions are as follows: sweep rate: 1 Hz, chip used:MFMR-20, lift height: 20 nm, and correction: Flatten order 3.

The servo pattern is a magnetized region, which is formed by magnetizinga specific region of the magnetic layer 43 in a specific direction by aservo writer during magnetic tape manufacture. In the servo band SB, aregion in which a servo pattern is not formed (hereinafter referred toas a “non-pattern region”) may be a magnetized region in which themagnetic layer 43 is magnetized or may be a non-magnetized region inwhich the magnetic layer 43 is not magnetized. In a case where thenon-pattern region is a magnetized region, the servo-pattern formedregion and the non-pattern region may be magnetized in differentdirections (for example, in directions opposite to each other).

In the LTO standard, a servo pattern including a plurality of servostripes (linear magnetized region) 113 inclined with respect to thewidth direction of the magnetic tape MT is formed in the servo band SBas illustrated in FIG. 6 .

The servo band SB includes a plurality of servo frames 110. Each servoframe 110 includes 18 servo stripes 113. Specifically, each servo frame110 includes a servo subframe 1 (111) and a servo subframe 2 (112).

The servo subframe 1 (111) is composed of an A burst 111A and a B burst111B. The B burst 111B is disposed adjacent to the A burst 111A. The Aburst 111A includes five servo stripes 113 formed at specifiedintervals, which are inclined at a predetermined angle φ with respect tothe width direction of the magnetic tape MT. In FIG. 6 , these fiveservo stripes 113 are indicated by the reference numerals A₁, A₂, A₃,A₄, and A₅ from the end of tape (EOT) to the beginning of tape (BOT) ofthe magnetic tape MT. Similar to the A burst 111A, the B burst 111Bincludes five servo pulses 63 formed at specified intervals, which areinclined at a predetermined angle φ with respect to the width directionof the magnetic tape MT. In FIG. 6 , these five servo stripes 113 areindicated by the reference numerals B₁, B₂, B₃, B₄, and B₅ from the EOTto the BOT of the magnetic tape MT. The servo stripe 113 of the B burst111B is inclined in the direction opposite to the servo stripe 113 ofthe A burst 111A. That is, the servo stripe 113 of the A burst 111A andthe servo stripe 113 of the B burst 111B are disposed in an invertedV-shape.

The servo subframe 2 (112) includes a C burst 112C and a D burst 112D.The D burst 112D is disposed adjacent to the C burst 112C. The C burst112C includes four servo stripes 113 formed at specified intervals,which are inclined at a predetermined angle φ with respect to the widthdirection of the tape. In FIG. 6 , these four servo stripes 113 areindicated by the reference numerals C₁, C₂, C₃, and C₄ from EOT to BOTof the magnetic tape MT. Like the C burst 112C, the D burst 112Dincludes four servo stripes 63 formed at specified intervals, which areinclined at a predetermined angle φ with respect to the width directionof the tape. In FIG. 6 , these four servo stripes 113 are indicated bythe reference numerals D₁, D₂, D₃, and D₄ from EOT to BOT of themagnetic tape MT. The servo stripe 113 of the D burst 112D and the servostripe 113 of the C burst 112C are inclined in directions opposite toeach other. That is, the servo stripe 113 of the C burst 112C and theservo stripe 113 of the D burst 112D are disposed in an invertedV-shape.

The predetermined angle φ of the servo stripe 113 in the A burst 111A,the B burst 111B, the C burst 112C, and the D burst 112D may be, forexample, 5° to 25°, and particularly 11° to 25°.

When the servo band SB is read in the magnetic head, information foracquiring the tape speed and the vertical position of the magnetic headcan be obtained. The tape speed is calculated from the time between fourtiming signals (A1-C1, A2-C2, A3-C3, A4-C4). The head position iscalculated from the time between the four timing signals and the timebetween other four timing signals (A1-B1, A2-B2, A3-B3, A4-B4).

As illustrated in FIG. 6 , it is preferable that the servo patterns(that is, the plurality of servo stripes 113) be linearly arranged inthe longitudinal direction of the magnetic tape MT. That is, it ispreferable that the servo band SB have a linear shape in thelongitudinal direction of the magnetic tape MT.

The upper limit value of the average thickness t_(m) of the magneticlayer 43 is 80 nm or less, preferably 70 nm or less, and more preferably50 nm or less. When the upper limit value of the average thickness t_(m)of the magnetic layer 43 is 80 nm or less, since the influence of thediamagnetic field can be reduced when a ring-type head is used as arecording head, it is possible to obtain better electromagneticconversion characteristics.

The lower limit value of the average thickness t_(m) of the magneticlayer 43 is preferably 35 nm or more. When the lower limit value of theaverage thickness t_(m) of the magnetic layer 43 is 35 nm or more, anoutput can be secured in a case where an MR type head is used as areproducing head, and thus it is possible to obtain more excellentelectromagnetic conversion characteristics.

The average thickness t_(m) of the magnetic layer 43 is obtained asfollows. First, the magnetic tape MT to be measured is processed by anFIB method or the like and sliced. When the FIB method is used, a carbonlayer and a tungsten layer are formed as protective films as apretreatment for observing a TEM image of a cross section to bedescribed below. The carbon layer is formed on the surface of themagnetic layer 43 and the surface of the back layer 44 of the magnetictape MT by a vapor deposition method, and the tungsten layer is thenadditionally formed on the surface of the magnetic layer 43 by a vapordeposition method or a sputtering method. The slicing is performed inthe length direction (longitudinal direction) of the magnetic tape MT.That is, according to the slicing, a cross section parallel to both thelongitudinal direction and the thickness direction of the magnetic tapeMT is formed.

The cross section of the obtained sliced sample is observed under atransmission electron microscope (TEM) according to the followingconditions to obtain a TEM image. Here, the magnification and theacceleration voltage may be appropriately adjusted according to the typeof the device.

-   Device: TEM (H9000NAR commercially available from Hitachi, Ltd.)-   Acceleration voltage: 300 kV-   Magnification: 100,000x

Next, using the obtained TEM image, the thickness of the magnetic layer43 is measured at positions of at least 10 points or more in thelongitudinal direction of the magnetic tape MT. The average valueobtained by simply averaging (taking an arithmetic mean of) the obtainedmeasured values is defined as the average thickness t_(m) [nm] of themagnetic layer 43. Here, the positions at which the measurement isperformed are randomly selected from the test piece.

Magnetic Powder

The magnetic powder contains a plurality of magnetic particles. Themagnetic particles are, for example, particles containing hexagonalferrite (hereinafter referred to as “hexagonal ferrite particles”),particles containing epsilon-type iron oxide (ε-iron oxide) (hereinafterreferred to as “ε-iron oxide particles”), or particles containingCo-containing spinel ferrite (hereinafter referred to as “cobalt ferriteparticles”). It is preferable that the magnetic powder becrystal-orientated preferentially in the vertical direction of themagnetic tape MT. In this specification, the vertical direction(thickness direction) of the magnetic tape MT is the thickness directionof the magnetic tape MT in a planar state.

Hexagonal Ferrite Particles

The hexagonal ferrite particles have, for example, a plate shape such asa hexagonal plate shape. In this specification, the hexagonal plateshape includes a substantially hexagonal plate shape. The hexagonalferrite preferably contains at least one of Ba, Sr, Pb and Ca, and morepreferably at least one of Ba and Sr. Specifically, the hexagonalferrite may be, for example, barium ferrite or strontium ferrite. Thebarium ferrite may further contain at least one of Sr, Pb and Ca inaddition to Ba. The strontium ferrite may further contain at least oneof Ba, Pb and Ca in addition to Sr.

More specifically, the hexagonal ferrite has an average compositionrepresented by a general formula of MFe₁₂O₁₉. Here, M is, for example,at least one metal of Ba, Sr, Pb and Ca, and preferably at least onemetal of Ba and Sr. M may be a combination of Ba, and at least one metalselected from the group consisting of Sr, Pb and Ca. In addition, M maybe a combination of Sr, and at least one metal selected from the groupconsisting of Ba, Pb and Ca. In the above general formula, some of Femay be replaced with other metal elements.

In a case where a magnetic powder contains hexagonal ferrite particlepowder, an average particle size of the magnetic powder is preferably 30nm or less, more preferably 12 nm or more and 25 nm or less, still morepreferably 15 nm or more and 22 nm or less, particularly preferably 15nm or more and 20 nm or less, and most preferably 15 nm or more and 18nm or less. When the average particle size of the magnetic powder is 30nm or less, it is possible to obtain more excellent electromagneticconversion characteristics (for example, SNR) in the magnetic tape MThaving a high recording density. On the other hand, when the averageparticle size of the magnetic powder is 12 nm or more, dispersibility ofthe magnetic powder is improved, and more excellent electromagneticconversion characteristics (for example, SNR) can be obtained.

In a case where the magnetic powder contains hexagonal ferrite particlepowder, an average aspect ratio of the magnetic powder may be, forexample, 1.0 or more and 3.0 or less. When the average aspect ratio ofthe magnetic powder is in a range between 1.0 or more and 3.0 or less,aggregation of the magnetic powder can be suppressed. In addition, whenthe magnetic powder is vertically oriented in the formation process ofthe magnetic layer 43, resistance to be applied to the magnetic powdercan be suppressed. Thus, a vertical orientation property of the magneticpowder can be improved. Further, in a case where the magnetic powdercontains hexagonal ferrite particle powder, the average aspect ratio ofthe magnetic powder is preferably 1.0 or more and 2.5 or less, morepreferably 1.0 or more and 2.1 or less, and still more preferably 1.0 ormore and 1.8 or less. When the average aspect ratio of the magneticpowder is in a range between 1.0 or more and 2.5 or less, aggregation ofthe magnetic powder can be further suppressed. In addition, when themagnetic powder is vertically oriented in the formation process of themagnetic layer 43, resistance to be applied to the magnetic powder canbe further suppressed. Thus, a vertical orientation property of themagnetic powder can be further improved.

In a case where the magnetic powder contains hexagonal ferrite particlepowder, the average particle size and the average aspect ratio of themagnetic powder are obtained as follows. First, the magnetic tape MT tobe measured is processed by an FIB method or the like and sliced. Whenthe FIB method is used, a carbon layer and a tungsten layer are formedas protective films as a pretreatment for observing a TEM image of across section to be described below. The carbon layer is formed on thesurface of the magnetic layer 43 and the surface of the back layer 44 ofthe magnetic tape MT by a vapor deposition method, and the tungstenlayer is then additionally formed on the surface of the magnetic layer43 by a vapor deposition method or a sputtering method. The slicing isperformed in the length direction (longitudinal direction) of themagnetic tape MT. That is, according to the slicing, a cross sectionparallel to both the longitudinal direction and the thickness directionof the magnetic tape MT is formed.

The cross section of the obtained sliced sample is observed such thatthe entire magnetic layer 43 is included in the thickness direction ofthe magnetic layer 43 with an acceleration voltage of 200 kV and a totalmagnification of 500,000x by using a transmission electron microscope(H-9500 manufactured by Hitachi High Technologies Co., Ltd.), and a TEMphotograph is captured. Next, 50 particles of which the sides areoriented toward an observation surface and the particle thickness can beclearly confirmed are selected from the captured TEM photograph. Forexample, an example of the TEM photograph is illustrated in FIGS. 7A and7B. In FIGS. 7A and 7B, for example, particles indicated by arrows a andd are selected because the thicknesses thereof can be clearly confirmed.A maximum plate thickness DA of each of the selected 50 particles ismeasured. An average maximum plate thickness DA_(ave) is obtained bysimply averaging (taking an arithmetic mean of) these maximum platethicknesses DA obtained in this manner. Subsequently, a plate diameterDB of each magnetic powder is measured. In order to measure the platediameter DB of the particle, 50 particles each of which the platediameter can be clearly confirmed are selected from the captured TEMphotograph. For example, in FIGS. 7A and 7B, for example, particlesindicated by arrows b and c are selected because the plate diametersthereof can be clearly confirmed. A plate diameter DB of each of theselected 50 particles is measured. An average plate diameter DB_(ave) isobtained by simply averaging (taking an arithmetic mean of) these platediameters DB. The average plate diameter DB_(ave) is an average particlesize. Then, an average aspect ratio (DB_(ave)/DA_(ave)) is obtained fromthe average maximum plate thickness DA_(ave) and the average platediameter DB_(ave).

In a case where the magnetic powder contains hexagonal ferrite particlepowder, an average particle volume of the magnetic powder is preferably5900 nm³ or less, more preferably 500 nm³ or more and 3400 nm³ or less,still more preferably 1000 nm³ or more and 2500 nm³ or less,particularly preferably 1000 nm³ or more and 1800 nm³ or less, and mostpreferably 1000 nm³ or more and 1600 nm³ or less. When the averageparticle volume of the magnetic powder is 5900 nm³ or less, the sameeffects as in a case where the average particle size of the magneticpowder is set to 30 nm or less are obtained. On the other hand, when theaverage particle volume of the magnetic powder is 500 nm³ or more, thesame effects as in a case where the average particle size of themagnetic powder is set to 12 nm or more are obtained.

The average particle volume of the magnetic powder is obtained asfollows.

First, as described with respect to the above-described method ofcalculating the average particle size of the magnetic powder, an averagemaximum plate thickness DA_(ave) and an average plate diameter DB_(ave)are obtained. Next, an average volume V of a magnetic powder is obtainedby the following formula.

$\text{V=}\frac{3\sqrt{3}}{8} \times \text{DA}_{\text{ave}} \times \text{DB}_{\text{ave}} \times \text{DB}_{\text{ave}}$

ε-Iron Oxide Particles

The ε-iron oxide particles are hard magnetic particles that allow a highcoercive force to be obtained even with fine particles. The ε-iron oxideparticles have a spherical shape or a cube shape. In this specification,the spherical shape includes a substantially spherical shape. Inaddition, the cube shape includes a substantially cube shape. Since theε-iron oxide particles have the above shape, when the ε-iron oxideparticles are used as magnetic particles, it is possible to reduce thecontact area between particles in the thickness direction of themagnetic tape MT and restrict aggregation of the particles, comparedwith when barium ferrite particles having a hexagonal plate shape areused as magnetic particles. Therefore, it is possible to improve thedispersibility of the magnetic powder, and obtain better electromagneticconversion characteristics (for example, SNR).

The ε-iron oxide particles have a core-shell type structure.Specifically, the ε-iron oxide particles have a core part and a shellpart having a two-layer structure provided around the core part. Theshell part having a two-layer structure has a first shell part providedon the core part and a second shell part provided on the first shellpart.

The core part contains ε-iron oxide. The ε-iron oxide contained in thecore part is preferably composed of ε—Fe₂O₃ crystal as a main phase, andmore preferably composed of single-phase ε—Fe₂O₃.

The first shell part covers at least a part of the periphery of the corepart. Specifically, the first shell part may partially cover theperiphery of the core part or may cover the entire periphery of the corepart. In order to make exchange coupling between the core part and thefirst shell part sufficient and improve magnetic characteristics, it ispreferable to cover the entire surface of the core part.

The first shell part is a so-called soft magnetic layer, and contains,for example, a soft magnetic component such as α—Fe, Ni—Fe alloys orFe—Si—Al alloys. α—Fe may be obtained by reducing the ε-iron oxidecontained in the core part.

The second shell part is an oxide film as an antioxidant layer. Thesecond shell part contains α-iron oxide, aluminum oxide or siliconoxide. The α-iron oxide includes, for example, at least one iron oxideamong Fe₃O₄, Fe₂O₃ and FeO. When the first shell part contains α—Fe(soft magnetic component), the α-iron oxide may be obtained by oxidizingα—Fe contained in the first shell part.

Since the ε-iron oxide particles have the first shell part as describedabove, a coercive force Hc of the core part alone is kept at a largevalue in order to secure thermal stability, and the coercive force Hc ofthe entire ε-iron oxide particles (core-shell particles) can be adjustedto a coercive force Hc suitable for recording. In addition, when theε-iron oxide particles have the second shell part as described above, ina process of producing the magnetic tape MT and before the process, itis possible to minimize deterioration of the characteristics of theε-iron oxide particles due to the ε-iron oxide particles being exposedto the air, and rust and the like being generated on the surfaces of theparticles. Therefore, it is possible to minimize deterioration ofcharacteristics of the magnetic tape MT.

The oxide particles may have a shell part having a single-layerstructure. In this case, the shell part has the same configuration asthe first shell part. Here, in order to minimize deterioration ofcharacteristics of the oxide particles, as described above, it ispreferable for the ε-iron oxide particles to have a shell part having atwo-layer structure.

The oxide particles may contain an additive in place of the core-shellstructure, or may contain an additive together with the core-shellstructure. In this case, some of Fe of the oxide particles is replacedwith an additive. Even when the oxide particles contain an additive,since the coercive force Hc of the entire ε-iron oxide particles can beadjusted to a coercive force Hc suitable for recording, it is possibleto improve ease of recording. The additive is a metal element other thaniron, preferably a trivalent metal element, more preferably at least oneof Al, Ga and In, and still more preferably at least one of Al and Ga.

Specifically, the oxide containing an additive is an ε—Fe_(2—x)M_(x)O₃crystal (where, M is a metal element other than iron, preferably atrivalent metal element, more preferably at least one of Al, Ga and In,and still more preferably at least one of Al and Ga. x is, for example,0 < x <1).

In a case where the magnetic powder contains ε-iron oxide particlepowder, the average particle size of the magnetic powder (averagemaximum particle size) is, for example, 22.5 nm or less. The averageparticle size of the magnetic powder (average maximum particle size) ispreferably 22 nm or less, more preferably 8 nm or more and 22 nm orless, still more preferably 12 nm or more and 22 nm or less,particularly preferably 12 nm or more and 15 nm or less, and mostpreferably 12 nm or more and 14 nm or less. In the magnetic tape MT, aregion having a size of ½ of the recording wavelength is the actualmagnetized region. For this reason, by setting the average particle sizeof the magnetic powder to half or less of the shortest recordingwavelength, more excellent electromagnetic conversion characteristics(for example, SNR) can be obtained. Thus, when the average particle sizeof the magnetic powder is 22 nm or less, more excellent electromagneticconversion characteristics (for example, SNR) can be obtained in amagnetic tape MT having a high recording density (for example, amagnetic tape MT) configured to be able to record a signal with ashortest recording wavelength of 44 nm or less. On the other hand, whenthe average particle size of the magnetic powder is 8 nm or more,dispersibility of the magnetic powder is improved, and more excellentelectromagnetic conversion characteristics (for example, SNR) can beobtained.

In a case where the magnetic powder contains ε-iron oxide particlepowder, an average aspect ratio of the magnetic powder may be preferably1.0 or more and 3.0 or less, more preferably 1.0 or more and 2.5 orless, still more preferably 1.0 or more and 2.1 or less, andparticularly preferably 1.0 or more and 1.8 or less. When the averageaspect ratio of the magnetic powder is in a range between 1.0 or moreand 3.0 or less, aggregation of the magnetic powder can be suppressed.In addition, when the magnetic powder is vertically oriented in theformation process of the magnetic layer 43, resistance to be applied tothe magnetic powder can be suppressed. Thus, a vertical orientationproperty of the magnetic powder can be improved.

In a case where the magnetic powder contains ε-iron oxide particlepowder, the average particle size and the average aspect ratio of themagnetic powder are obtained as follows. First, the magnetic tape MT tobe measured is processed by a focused ion beam (FIB) method or the likeand sliced. When the FIB method is used, a carbon layer and a tungstenlayer are formed as protective films as a pretreatment for observing aTEM image of a cross section to be described below. The carbon layer isformed on the surface of the magnetic layer 43 and the surface of theback layer 44 of the magnetic tape MT by a vapor deposition method, andthe tungsten layer is then additionally formed on the surface of themagnetic layer 43 by a vapor deposition method or a sputtering method.The slicing is performed in the length direction (longitudinaldirection) of the magnetic tape MT. That is, according to the slicing, across section parallel to both the longitudinal direction and thethickness direction of the magnetic tape MT is formed.

The cross section of the obtained sliced sample is observed such thatthe entire magnetic layer 43 is included in the thickness direction ofthe magnetic layer 43 with an acceleration voltage of 200 kV and a totalmagnification of 500,000x by using a transmission electron microscope(H-9500 manufactured by Hitachi High Technologies Co., Ltd.), and a TEMphotograph is captured. Next, 50 particles of which the particle shapescan be clearly confirmed are selected from the captured TEM photograph,and a major axis length DL and a minor axis length DS of each particleare measured. Here, the major axis length DL is a maximum distance(so-called maximum ferret diameter) among distances between two parallellines drawn from all angles so as to be in contact with the contour ofeach particle. On the other hand, the minor axis length DS is a maximumlength among lengths of particles in a direction perpendicular to amajor axis (DL) of a particle. Subsequently, an average major axislength DL_(ave) is obtained by simply averaging (taking an arithmeticmean of) these major axis lengths DL of the measured 50 particles. Theaverage major axis length DL_(ave) obtained in this manner is set to bean average particle size of the magnetic powder. In addition, an averageminor axis length DS_(ave) is obtained by simply averaging (taking anarithmetic mean of) these minor axis lengths DS of the measured 50particles. Then, an average aspect ratio (DL_(ave)/DS_(ave)) of aparticle is obtained from the average major axis length DL_(ave) and theaverage minor axis length DSave.

In a case where the magnetic powder contains ε-iron oxide particlepowder, an average particle volume of the magnetic powder is preferably5600 nm³ or less, more preferably 250 nm³ or more and 3300 nm³ or less,still more preferably 900 nm³ or more and 2500 nm³ or less, particularlypreferably 900 nm³ or more and 1800 nm³ or less, and most preferably 900nm³ or more and 1600 nm³ or less. In general, the noise of the magnetictape MT is inversely proportional to the square root of the number ofparticles (that is, proportional to the square root of the particlevolume), and thus more excellent electromagnetic conversioncharacteristics (for example, SNR) can be obtained by making theparticle volume smaller. Thus, when the average particle volume of themagnetic powder is 5600 nm³ or less, more excellent electromagneticconversion characteristics (for example, SNR) can be obtained similarlyto a case where the average particle size of the magnetic powder is setto 22 nm or less. On the other hand, when the average particle volume ofthe magnetic powder is 250 nm³ or more, the same effects as in a casewhere the average particle size of the magnetic powder is set to 8 nm ormore are obtained.

In a case where the ε-iron oxide particle has a spherical shape, theaverage particle volume of the magnetic powder is obtained as follows.First, an average major axis length DL_(ave) is obtained in the samemanner as in the method of calculating the average particle size of themagnetic powder. Next, an average volume V of the magnetic powder isobtained by the following formula.

V=(Π/6) × DL_(ave)³

In a case where the ε-iron oxide particle has a cube shape, the averagevolume of the magnetic powder is obtained as follows. The magnetic tapeMT is processed by a focused ion beam (FIB) method or the like andsliced. When the FIB method is used, a carbon film and a tungsten thinfilm are formed as protective films as a pretreatment for observing aTEM image of a cross section to be described below. The carbon film isformed on the surface of the magnetic layer 43 and the surface of theback layer 44 of the magnetic tape MT by a vapor deposition method, andthe tungsten thin film is then additionally formed on the surface of themagnetic layer 43 by a vapor deposition method or a sputtering method.The slicing is performed in the length direction (longitudinaldirection) of the magnetic tape MT. That is, according to the slicing, across section parallel to both the longitudinal direction and thethickness direction of the magnetic tape MT is formed.

The cross section of the obtained sliced sample is observed such thatthe entire magnetic layer 43 is included in the thickness direction ofthe magnetic layer 43 with an acceleration voltage of 200 kV and a totalmagnification of 500,000x by using a transmission electron microscope(H-9500 manufactured by Hitachi High Technologies Co., Ltd.), and a TEMphotograph is captured. Here, the magnification and the accelerationvoltage may be appropriately adjusted according to the type of thedevice. Next, 50 particles having a clear particle shape are selectedfrom the captured TEM photograph, and a side length DC of each particleis measured. Subsequently, an average side length DC_(ave) is obtainedby simply averaging (taking an arithmetic mean of) these side lengths DCof the measured 50 particles. Next, an average volume V_(ave) of themagnetic powder (particle volume) is obtained from the following formulausing the average side length DC_(ave).

V_(ave) = DC_(ave)³

Cobalt Ferrite Particles

The cobalt ferrite particles preferably have uniaxial crystalanisotropy. When the cobalt ferrite particles have uniaxial crystalanisotropy, the magnetic powder can be crystal-oriented preferentiallyin the vertical direction of the magnetic tape MT. The cobalt ferriteparticles have, for example, a cube shape. In this specification, thecube shape includes a substantially cube shape. The Co-containing spinelferrite may further contain at least one of Ni, Mn, Al, Cu and Zn inaddition to Co.

The Co-containing spinel ferrite has, for example, an averagecomposition represented by the following formula.

(where, in the formula, M is at least one metal among, for example, Ni,Mn, Al, Cu, and Zn. x is a value in a range of 0.4 ≤x ≤1.0. y is a valuein a range of 0 ≤ y ≤ 0.3. Here, x and y satisfy a relationship of (x +y) ≤1.0. z is a value in a range of 3 ≤z ≤4. A portion of Fe may bereplaced with other metal elements.)

In a case where the magnetic powder contains cobalt ferrite particlepowder, the average particle size of the magnetic powder is preferably25 nm or less, more preferably 8 nm or more and 23 nm or less, stillmore preferably 8 nm or more and 12 nm or less, and particularlypreferably 8 nm or more and 11 nm or less. When the average particlesize of the magnetic powder is 25 nm or less, more excellentelectromagnetic conversion characteristics (for example, SNR) can beobtained in the magnetic tape MT having a high recording density. On theother hand, when the average particle size of the magnetic powder is 8nm or more, dispersibility of the magnetic powder is improved, and moreexcellent electromagnetic conversion characteristics (for example, SNR)can be obtained. A method of calculating the average particle size ofthe magnetic powder is the same as a method of calculating the averageparticle size of the magnetic powder in a case where the magnetic powdercontains ε-iron oxide particle powder.

In a case where the magnetic powder contains cobalt ferrite particlepowder, the average aspect ratio of the magnetic powder is preferably1.0 or more and 3.0 or less, more preferably 1.0 or more and 2.5 orless, still more preferably 1.0 or more and 2.1 or less, andparticularly preferably 1.0 or more and 1.8 or less. When the averageaspect ratio of the magnetic powder is in a range between 1.0 or moreand 3.0 or less, aggregation of the magnetic powder can be suppressed Inaddition, when the magnetic powder is vertically oriented in theformation process of the magnetic layer 43, resistance to be applied tothe magnetic powder can be suppressed. Thus, a vertical orientationproperty of the magnetic powder can be improved. A method of calculatingthe average aspect ratio of the magnetic powder is the same as a methodof calculating the average aspect ratio of the magnetic powder in a casewhere the magnetic powder contains ε-iron oxide particle powder.

In a case where the magnetic powder contains cobalt ferrite particlepowder, the average particle volume of the magnetic powder is preferably15000 nm³ or less, more preferably 500 nm³ or more and 3500 nm³ or less,still more preferably 500 nm³ or more and 2500 nm³ or less, particularlypreferably 500 nm³ or more and 1800 nm³ or less, and most preferably 500nm³ or more and 1600 nm³ or less. When the average particle volume ofthe magnetic powder is 15000 nm³ or less, the same effects as in a casewhere the average particle size of the magnetic powder is set to 25 nmor less are obtained. On the other hand, when the average particlevolume of the magnetic powder is 500 nm³ or more, the same effects as ina case where the average particle size of the magnetic powder is set to8 nm or more are obtained. A method of calculating the average particlevolume of the magnetic powder is the same as a method of calculating anaverage particle volume in a case where a oxide particle has a cubeshape.

Binding Agent

Examples of binding agents include a thermoplastic resin, athermosetting resin, and a reactive resin. Examples of thermoplasticresins include vinyl chloride, vinyl acetate, vinyl chloride-vinylacetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinylchloride-acrylonitrile copolymers, acrylic acid ester-acrylonitrilecopolymers, acrylic acid ester-vinyl chloride-vinylidene chloridecopolymers, acrylic acid ester-acrylonitrile copolymers, acrylic acidester-vinylidene chloride copolymers, methacrylic acid ester-vinylidenechloride copolymers, methacrylic acid ester-vinyl chloride copolymers,methacrylic acid ester-ethylene copolymers, polyvinyl fluoride,vinylidene chloride-acrylonitrile copolymers, acrylonitrile-butadienecopolymers, polyamide resins, polyvinyl butyral, cellulose derivatives(cellulose acetate butyrate, cellulose diacetate, cellulose triacetate,cellulose propionate, nitrocellulose), styrene butadiene copolymers,polyurethane resins, polyester resins, amino resins, and syntheticrubber.

Examples of thermosetting resins include phenolic resins, epoxy resins,polyurethane curable resins, urea resins, melamine resins, alkyd resins,silicone resins, polyamine resins, and urea formaldehyde resins.

In all of the above-described binding agent, for the purpose ofimproving dispersibility of the magnetic powder, —SO₃M, —OSO₃M, —COOM, P= O(OM)₂ (where, M in the formula represents a hydrogen atom or analkali metal such as lithium, potassium, or sodium), a side-chain aminehaving a terminal group represented by —NR1R2, —NR1R2R3⁺X^(—), amain-chain amine represented by > NR1R2⁺X⁻ (where, R1, R2, and R3 in theformula represent a hydrogen atom or a hydrocarbon group, and X⁻represents halogen element ions such as fluorine, chlorine, bromine andiodine, inorganic ions, or organic ions.), and a polar functional groupsuch as —OH, —SH, —CN, or an epoxy group may be introduced. The amountof these polar functional groups introduced into the binding agent ispreferably 10⁻¹ to 10⁻⁸ mol/g and more preferably 10⁻² to 10⁻⁶ mol/g.

Lubricant

The lubricant contains, for example, at least one selected from amongfatty acids and fatty acid esters, and preferably contains both fattyacids and fatty acid esters. When the magnetic layer 43 contains alubricant, particularly, when the magnetic layer 43 contains both fattyacids and fatty acid esters, this contributes to improving the runningstability of the magnetic tape MT. More particularly, when the magneticlayer 43 contains a lubricant and has pores, a good running stability isachieved. It is considered that running stability is improved because adynamic friction coefficient of the surface of the magnetic tape MT onthe magnetic layer 43 side is adjusted to a value suitable for therunning of the magnetic tape MT by the lubricant.

The fatty acid is preferably a compound represented by the followingGeneral Formula (1) or (2). For example, one or both of the compoundrepresented by the following General Formula (1) and the compoundrepresented by General Formula (2) may be contained as the fatty acid.

In addition, the fatty acid ester is preferably a compound representedby the following General Formula (3) or (4). For example, one or both ofthe compound represented by the following General Formula (3) and thecompound represented by General Formula (4) may be contained as thefatty acid ester.

When the lubricant contains one or both of the compound represented byGeneral Formula (1) and the compound represented by General Formula (2),and one or both of the compound represented by General Formula (3) andthe compound represented by General Formula (4), it is possible tominimize an increase in the dynamic friction coefficient due to repeatedrecording or reproducing of the magnetic tape MT.

(where, in General Formula (1), k is an integer selected from the rangeof 14 or more and 22 or less, and more preferably selected from therange of 14 or more and 18 or less).

(where, in General Formula (2), a sum of n and m is an integer selectedfrom the range of 12 or more and 20 or less, and more preferablyselected from the range of 14 or more and 18 or less).

(where, in General Formula (3), p is an integer selected from the rangeof 14 or more and 22 or less, and more preferably selected from therange of 14 or more and 18 or less, and q is an integer selected fromthe range of 2 or more and 5 or less, and more preferably selected fromthe range of 2 or more and 4 or less).

(where, in General Formula (4), r is an integer selected from the rangeof 14 or more and 22 or less, and s is an integer selected from therange of 1 or more and 3 or less).

Antistatic Agent

Examples of antistatic agents include carbon black, a naturalsurfactant, a nonionic surfactant, and a cationic surfactant.

Abrasive

Examples of abrasives include α-alumina with an α transformation rate of90% or more, β-alumina, y-alumina, silicon carbide, chromium oxide,cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide,titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungstenoxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate,calcium sulfate, barium sulfate, molybdenum disulfide, needle-shapedα-iron oxides obtained by dehydrating and annealing raw materials ofmagnetic iron oxide, and those obtained by performing a surfacetreatment on the above materials with aluminum and/or silica asnecessary.

Curing Agent

Examples of curing agents include polyisocyanate. Examples ofpolyisocyanates include aromatic polyisocyanates such as adducts oftolylene diisocyanate (TDI) and an active hydrogen compound, andaliphatic polyisocyanates such as adducts of hexamethylene diisocyanate(HMDI) and an active hydrogen compound. The weight-average molecularweight of these polyisocyanates is preferably in a range of 100 to3,000.

Antirust Agent

Examples of antirust agents include phenols, naphthols, quinones,heterocyclic compounds containing nitrogen atoms, heterocyclic compoundscontaining oxygen atoms, and heterocyclic compounds containing sulfuratoms.

Non-Magnetic Reinforcing Particles

Examples of non-magnetic reinforcing particles include aluminum oxide(α, β or Y alumina), chromium oxide, silicon oxide, diamond, garnet,emery, boron nitride, titanium carbide, silicon carbide, titaniumcarbide, and titanium oxide (rutile type or anatase type titaniumoxide).

Underlayer

The underlayer 42 is provided to alleviate the unevenness of the surfaceof the substrate 41 and adjust the unevenness of the surface of themagnetic layer 43. The underlayer 42 is a non-magnetic layer containinga non-magnetic powder, a binding agent and a lubricant. According to theunderlayer 42, the lubricant is supplied to the surface of the magneticlayer 43. The underlayer 42 may further contain at least one additiveamong an antistatic agent, a curing agent, an antirust agent, and thelike, as necessary.

An average thickness of the underlayer 42 is preferably 0.3 µm or moreand 2.0 µm or less, and more preferably 0.5 µm or more and 1.4 µm orless. Here, the average thickness of the underlayer 42 is obtained inthe same manner as in the average thickness t_(m) of the magnetic layer43. Here, the magnification of the TEM image is appropriately adjustedaccording to the thickness of the underlayer 42. When the averagethickness of the underlayer 42 is 2.0 µm or less, the degree ofexpansion and contraction of the magnetic tape MT is larger due to anexternal force, and thus it is easier to adjust the width of themagnetic tape MT by adjusting the tension.

It is preferable that the underlayer 42 have a plurality of holeportions. When a lubricant is stored in the plurality of hole portions,it is possible to further suppress a decrease in the amount of lubricantsupplied between the surface of the magnetic layer 43 and the magnetichead even after recording or reproduction is repeatedly performed (thatis, even after the magnetic head is brought into contact with thesurface of the magnetic tape MT and runs repeatedly). Thus, it ispossible to further suppress an increase in a dynamic frictioncoefficient. That is, a more excellent running stability can beobtained.

Non-Magnetic Powder

The non-magnetic powder contains, for example, at least one of inorganicparticle powder and inorganic particle powder. In addition, thenon-magnetic powder may contain carbon powder such as carbon black.Here, one type of non-magnetic powder may be used alone, or two or moretypes of non-magnetic powders may be used in combination. Examples ofinorganic particles include metals, metal oxides, metal carbonates,metal sulfates, metal nitrides, metal carbides and metal sulfides.Examples of shapes of non-magnetic powders include various shapes suchas a needle shape, a spherical shape, a cube shape, and a plate shape,but the present disclosure is not limited to these shapes.

Binding Agent and Lubricant

The binding agent and the lubricant are the same as those of the abovemagnetic layer 43.

Additive

The antistatic agent, the curing agent and the antirust agent are thesame as those of the above magnetic layer 43.

Back Layer

The back layer 44 contains a binding agent and a non-magnetic powder.The back layer 44 may further contain at least one additive among alubricant, a curing agent, an antistatic agent, and the like, asnecessary. The binding agent and the non-magnetic powder are the same asthose of the above underlayer 42.

The average particle size of the non-magnetic powder is preferably 10 nmor more and 150 nm or less, and more preferably 15 nm or more and 110 nmor less. The average particle size of the non-magnetic powder isobtained in the same manner as the above-described average particle sizeof the magnetic powder. The non-magnetic powder may contain anon-magnetic powder having a particle size distribution of 2 or more.

An upper limit value of an average thickness of the back layer 44 ispreferably 0.6 µm or less. When the upper limit value of the averagethickness of the back layer 44 is 0.6 µm or less, the thicknesses of theunderlayer 42 and the substrate 41 can be kept large even when anaverage thickness of the magnetic tape MT is 5.6 µm or less, and thusrunning stability in the recording/reproducing device of the magnetictape MT can be maintained. A lower limit value of an average thicknessof the back layer 44 is not particularly limited, but is, for example,0.2 µm or more.

The average thickness t_(b) of the back layer 44 is obtained as follows.First, the average thickness t_(T) of the magnetic tape MT is measured.The method of measuring the average thickness t_(T) is as described inthe following “Average thickness of magnetic tape”. Subsequently, theback layer 44 of the sample is removed with a solvent such as methylethyl ketone (MEK) or diluted hydrochloric acid. Next, the thickness ofthe sample is measured at positions of 5 or more points using the LaserHologage (LGH-110C) (commercially available from Mitutoyo), and theaverage value t_(B) [µm] is calculated by simply averaging (taking anarithmetic mean of) these measured values. Then, the average thicknesst_(b) [µm] of the back layer 44 is obtained from the following formula.Here, the measurement positions are randomly selected from the sample.

t_(b)[μm] = t_(T)[μm]-t_(B)[μm]

Average Thickness of Magnetic Tape

An upper limit value of an average thickness (average total thickness)t_(T) of the magnetic tape MT is 5.3 µm or less, preferably 5.0 µm orless, more preferably 4.6 µm or less, and still more preferably 4.4 µmor less. When average thickness t_(T) of the magnetic tape MT is 5.3 µmor less, the recording capacity that can be recorded in one datacartridge can be increased as compared with a general magnetic tape. Alower limit value of an average thickness t_(T) of the magnetic tape MTis not particularly limited, but is, for example, 3.5 µm or more.

The average thickness t_(T) of the magnetic tape MT is obtained asfollows. First, a magnetic tape MT is prepared and cut to a length of250 mm to prepare a sample. Next, the thickness of the sample ismeasured at positions of 5 or more points using the Laser Hologage(LGH-110C) (commercially available from Mitutoyo) as a measurementdevice, and the average value t_(T) [µm] is calculated by simplyaveraging (taking an arithmetic mean of) these measured values. Here,the measurement positions are randomly selected from the sample.

Coercive Force Hc

An upper limit value of a coercive force Hc2 of the magnetic layer 43 inthe longitudinal direction of the magnetic tape MT is preferably 2,000Oe or less, more preferably 1,900 Oe or less, and still more preferably1,800 Oe or less. When the coercive force Hc2 of the magnetic layer 43in the longitudinal direction of the magnetic tape MT is 2,000 Oe orless, sufficient electromagnetic conversion characteristics can beprovided even at a high recording density.

The lower limit value of the coercive force Hc2 of the magnetic layer 43measured in the longitudinal direction of the magnetic tape MT ispreferably 1,000 Oe or more. When the coercive force Hc2 of the magneticlayer 43 measured in the longitudinal direction of the magnetic tape MTis 1,000 Oe or more, demagnetization due to leakage flux from therecording head can be minimized.

The coercive force Hc2 is obtained as follows. First, three sheets ofthe magnetic tape MT are superimposed on each other with a double-sidedtape and are then punched out with a punch of φ6.39 mm to prepare ameasurement sample. In this case, marking is performed with an arbitrarynon-magnetic ink so that the longitudinal direction (running direction)of the magnetic tape MT can be recognized. Then, an M-H loop of themeasurement sample (the entire magnetic tape MT) corresponding to thelongitudinal direction (running direction) of the magnetic tape MT ismeasured using a vibrating sample magnetometer (VSM). Next, coatingfilms (the underlayer 42, the magnetic layer 43, the back layer 44 andthe like) are wiped off with acetone, ethanol or the like, and only thesubstrate 41 remains. Then, three sheets of the obtained substrate 41are superimposed on each other with a double-sided tape and are thenpunched out with a punch of φ6.39 mm to prepare a sample for backgroundcorrection (hereinafter, referred to simply as “correction sample”).Thereafter, an M-H loop of the correction sample (the substrate 41)corresponding to the longitudinal direction of the substrate 41 (thelongitudinal direction of the magnetic tape MT) is measured using a VSM.

A high sensitivity vibrating sample magnetometer “Type VSM-P7-15”(commercially available from Toei Industry Co., Ltd.) is used formeasuring the M-H loop of the measurement sample (the entire magnetictape MT) and the M-H loop of the sample for correction (the substrate41). The measurement conditions are as follows: measurement mode: fullloop, maximum magnetic field: 15 kOe, magnetic field step: 40 bit, Timeconstant of Locking amp: 0.3 sec, Waiting time: 1 sec, and MH averagenumber: 20.

After the M-H loop of the measurement sample (the entire magnetic tapeMT) and the M-H loop of the sample for correction (the substrate 41) areobtained, the M-H loop of the sample for correction (the substrate 41)is subtracted from the M-H loop of the measurement sample (the entiremagnetic tape MT) to perform background correction, and the M-H loopafter background correction is obtained. A measurement/analysis programbundled in “Type VSM-P7-15” is used for calculating this backgroundcorrection. The coercive force Hc2 is obtained from the obtained M-Hloop after background correction. Here, for this calculation, ameasurement/analysis program bundled in “Type VSM-P7-15” is used. Notethat it is assumed that all of the above-described M-H loop measurementsare performed at 25° C. and 50% RH ± 5% RH. In addition, “diamagneticfield correction” when the M-H loop is measured in the longitudinaldirection of the magnetic tape MT is not performed.

Squareness Ratio

The squareness ratio S1 of the magnetic layer 43 in the verticaldirection of the magnetic tape MT is preferably 65% or more, morepreferably 70% or more, still more preferably 75% or more, particularlypreferably 80% or more, and most preferably 85% or more. When thesquareness ratio S1 is 65% or more, since the vertical orientation ofthe magnetic powder is sufficiently improved, it is possible to obtainbetter electromagnetic conversion characteristics.

The squareness ratio S1 in the vertical direction of the magnetic tapeMT is obtained as follows. First, three sheets of the magnetic tape MTare superimposed on each other with a double-sided tape and are thenpunched out with a punch of φ6.39 mm to prepare a measurement sample. Inthis case, marking is performed with an arbitrary non-magnetic ink sothat the longitudinal direction (running direction) of the magnetic tapeMT can be recognized. Then, an M-H loop of the measurement sample (theentire magnetic tape MT) corresponding to the vertical direction(thickness direction) of the magnetic tape MT is measured using the VSM.Next, coating films (the underlayer 42, the magnetic layer 43, the backlayer 44 and the like) are wiped off with acetone, ethanol or the like,and only the substrate 41 remains. Then, three sheets of the obtainedsubstrate 41 are superimposed on each other with a double-sided tape andare then punched out with a punch of φ6.39 mm to prepare a sample forbackground correction (hereinafter, referred to simply as “correctionsample”). Then, an M-H loop of the sample for correction (the substrate41) corresponding to the vertical direction (the vertical direction ofthe magnetic tape MT) of the substrate 41 is measured using the VSM.

A high sensitivity vibrating sample magnetometer “Type VSM-P7-15”(commercially available from Toei Industry Co., Ltd.) is used formeasuring the M-H loop of the measurement sample (the entire magnetictape MT) and the M-H loop of the sample for correction (the substrate41). The measurement conditions are as follows: measurement mode: fullloop, maximum magnetic field: 15 kOe, magnetic field step: 40 bit, Timeconstant of Locking amp: 0.3 sec, Waiting time: 1 sec, and MH averagenumber: 20.

After the M-H loop of the measurement sample (the entire magnetic tapeMT) and the M-H loop of the sample for correction (the substrate 41) areobtained, the M-H loop of the sample for correction (the substrate 41)is subtracted from the M-H loop of the measurement sample (the entiremagnetic tape MT) to perform background correction, and the M-H loopafter background correction is obtained. A measurement/analysis programbundled in “Type VSM-P7-15” is used for calculating this backgroundcorrection.

A saturation magnetization Ms (emu) and a residual magnetization Mr(emu) of the obtained M-H loop after background correction aresubstituted into the following formula, and the squareness ratio S1 (%)is calculated. Note that it is assumed that all of the above-describedM-H loop measurements are performed at 25° C. and 50% RH ± 5% RH. Inaddition, “diamagnetic field correction” when the M-H loop is measuredin the vertical direction of the magnetic tape MT is not measured. Here,for this calculation, a measurement/analysis program bundled in “TypeVSM-P7-15” is used.

squareness ratioS1(%) = (Mr/Ms) × 100

The squareness ratio S2 of the magnetic layer 43 in the longitudinaldirection (running direction) of the magnetic tape MT is preferably 35%or less, more preferably 30% or less, still more preferably 25% or less,particularly preferably 20% or less, and most preferably 15% or less.When the squareness ratio S2 is 35% or less, since the verticalorientation of the magnetic powder is sufficiently improved, it ispossible to obtain better electromagnetic conversion characteristics.

The squareness ratio S2 in the longitudinal direction of the magnetictape MT is obtained in the same manner as the squareness ratio S1 exceptthat the M-H loop is measured in the longitudinal direction (runningdirection) of the magnetic tape MT and the substrate 41.

Hc2/Hc1

A ratio Hc2/Hc1 between a coercive force Hc1 of the magnetic layer 43 inthe vertical direction of the magnetic tape MT and a coercive force Hc2of the magnetic layer 43 in the longitudinal direction of the magnetictape MT satisfies relationships of preferably Hc2/Hc1 ≤0.8, morepreferably Hc2/Hc1 ≤0.75, still more preferably Hc2/Hc1 ≤0.7,particularly preferably Hc2/Hc1 ≤0.65, and most preferably Hc2/Hc1 ≤0.6.When the coercive forces Hc1 and Hc2 satisfy a relationship of Hc2/Hc1≤0.8, the degree of vertical orientation of the magnetic powder can beincreased. Therefore, the magnetization transition width can be reducedand a high-output signal can be obtained during signal reproduction, andthus it is possible to obtain better electromagnetic conversioncharacteristics. Here, as described above, when Hc2 is small, sincemagnetization reacts with high sensitivity due to a magnetic field inthe vertical direction from the recording head, it is possible to form afavorable recording pattern.

In a case where the ratio Hc2/Hc1 is Hc2/Hc1 ≤0.8, it is particularlyeffective that the average thickness t_(m) of the magnetic layer 43 is90 nm or less. When the average thickness t_(m) of the magnetic layer 43exceeds 90 nm, the lower region (a region on the side of the underlayer42) of the magnetic layer 43 may be magnetized in the longitudinaldirection of the magnetic tape MT in a case where a ring-type head isused as the recording head, which results in a concern that the magneticlayer 43 may not be uniformly magnetized in the thickness direction.Thus, even when the ratio Hc2/Hc1 is set to be Hc2/Hc1 ≤0.8 (that is,even when the degree of vertical orientation of the magnetic powder isincreased), there is a concern that more excellent electromagneticconversion characteristics may not be obtained.

A lower limit value of Hc2/Hc1 is not particularly limited, but is, forexample, 0.5 ≤Hc2/Hc1. Here, the Hc2/Hc1 indicates a degree of verticalorientation of the magnetic powder, and a small Hc2/Hc1 indicates ahigher degree of vertical orientation of the magnetic powder.

A method of calculating the coercive force Hc2 of the magnetic layer 43in the longitudinal direction of the magnetic tape MT is as describedabove. The coercive force Hc1 of the magnetic layer 43 in the verticaldirection of the magnetic tape MT is obtained in the same manner as thecoercive force Hc2 of the magnetic layer 43 in the longitudinaldirection of the magnetic tape MT except that an M-H loop is measured inthe vertical direction (thickness direction) of the magnetic tape MT andthe substrate 41.

Activation Volume V_(act)

An activation volume V_(act) is preferably 8000 nm³ or less, morepreferably 6000 nm³ or less, still more preferably 5000 nm³ or less,particularly preferably 4000 nm³ or less, and most preferably 3000 nm³or less. When the activation volume V_(act) is 8000 nm³ or less, adispersed state of the magnetic powder is improved, and thus it ispossible to make a bit inversion region steep and to suppressdeterioration of a magnetization signal recorded on an adjacent trackdue to a leakage magnetic field from the recording head. Thus, there isa concern that more excellent electromagnetic conversion characteristicsmay not be obtained.

The above-described activation volume V_(act) is obtained by thefollowing formula derived by Street & Woolley.

V_(act)(nm³)  = k_(B)  ×  T  ×  X_(irr)/(μ₀  ×  Ms  × S)

(where, k_(B): Boltzmann constant (1.38 × 10⁻²³ J/K), T: temperature(K), X_(irr): irreversible magnetic susceptibility, µ₀: magneticpermeability of vacuum, S: magnetic viscosity coefficient, Ms:saturation magnetization (emu/cm³))

The irreversible magnetic susceptibility X_(irr), the saturationmagnetization Ms, and the magnetic viscosity coefficient S substitutedin the above-described formula are obtained by using a VSM as follows.Note that a measurement direction of the VSM is set to be the verticaldirection (thickness direction) of the magnetic tape MT. In addition, itis assumed that measurement using the VSM is performed at 25° C. and 50%RH ± 5% RH on a measurement sample cut out from the magnetic tape MThaving a long shape. In addition, it is assumed that “diamagnetic fieldcorrection” at the time of measuring the M-H loop in the verticaldirection of the magnetic tape MT is not measured.

Irreversible Magnetic Susceptibility X_(irr)

The irreversible magnetic susceptibility X_(irr) is defined as aninclination near a residual coercive force Hr in an inclination of aresidual magnetization curve (DCD curve). First, a magnetic field of-1193 kA/m (15 kOe) is applied to the entire magnetic tape MT and isthen returned to zero to set a residual magnetization state. Thereafter,a magnetic field of approximately 15.9 kA/m (200 Oe) is applied in theopposite direction and is then returned to zero to measure a residualmagnetization amount. Thereafter, similarly, measurement of applying amagnetic field 15.9 kA/m larger than the applied magnetic field andreturning it to zero is repeatedly performed, and a residualmagnetization amount is plotted with respect to the applied magneticfield to measure a DCD curve. From the obtained DCD curve, a point wherethe amount of magnetization is set to zero is defined as a residualcoercive force Hr, and the DCD curve is further differentiated to obtainan inclination of the DCD curve in each magnetic field. In theinclination of the DCD curve, an inclination near the residual coerciveforce Hr is X_(irr).

Saturation Magnetization Ms

First, an M-H loop after background correction is obtained in the samemanner as the above-described method of measuring the squareness ratioS1. Next, Ms (emu/cm³) is calculated from the value of saturationmagnetization Ms (emu) of the obtained M-H loop and the volume (cm³) ofthe magnetic layer 43 in the measurement sample. Note that the volume ofthe magnetic layer 43 is obtained by multiplying the area of themeasurement sample by an average thickness t_(m) of the magnetic layer43. A method of calculating the average thickness t_(m) of the magneticlayer 43 which is necessary for the calculation of the volume of themagnetic layer 43 is as described above.

Magnetic Viscosity Coefficient S

First, a magnetic field of -1193 kA/m (15 kOe) is applied to the entiremagnetic tape MT (measurement sample) and is then returned to zero toset a residual magnetization state. Thereafter, a magnetic field havinga value equal to the value of the residual coercive force Hr obtainedfrom the DCD curve is applied in the opposite direction. The amount ofmagnetization is continuously measured at fixed time intervals for 1000seconds in a state where a magnetic field has been applied. The magneticviscosity coefficient S is calculated by comparing a relationshipbetween a time t and the amount of magnetization M(t), which is obtainedin this manner, with the following formula. M(t) = M0+S × ln(t) (where,M(t): amount of magnetization for time t, M0: initial amount ofmagnetization, S: magnetic viscosity coefficient, ln(t): naturallogarithm of time)

Surface Roughness R_(b) of Back Surface

It is preferable that a surface roughness of a back surface (surfaceroughness of the back layer 44) R_(b) be R_(b) ≤ 6.0 [nm]. When thesurface roughness R_(b) of the back surface is in the above-describedrange, more excellent electromagnetic conversion characteristics can beobtained.

The surface roughness R_(b) of the back surface is obtained as follows.First, a magnetic tape MT with a width of 12.65 mm is prepared and cutto a length of 100 mm to prepare a sample. Next, the sample is placed ona slide glass so that a surface to be measured (the surface on themagnetic layer side) faces upward, and an end of the sample is fixedwith a mending tape. A surface shape is measured using VertScan (50xobjective lens) as a measurement device, and a surface roughness R_(b)of a back surface is obtained from the following formula based on theISO 25178 standard.

-   Device: non-contact roughness meter using optical interference-   (Non-contact surface/layer cross-sectional shape measurement system    VertScan R5500GL-M100-AC manufactured by Ryoka System Co., Ltd.)-   Objective lens: 20x-   Measurement region: 640 x480 pixels (field of view: approximately    237 µm × 178 µm field of view)-   Measurement mode: phase-   Wavelength filter: 520 nm-   CCD: ⅓ lens-   Noise removal filter: smoothing 3×3-   Surface correction: Correction with quadratic polynomial    approximation surface-   Measurement software: VS-Measure Version 5.5.2-   Analysis software: VS-viewer Version 5.5.5

$S_{\text{a}}\,\, = \,\,\frac{\text{1}}{\text{A}}\,{\int\limits_{\text{A}}{\int{\text{|}\,\text{Z}\,\left( {\text{x,}\,\text{y}\,} \right)}}}\,\text{|}\,\text{dxdy}$

As described above, after a surface roughness is measured at at least 5points in the longitudinal direction of the magnetic tape MT, theaverage value of each arithmetic mean roughness S_(a) (nm) automaticallycalculated from a surface profile obtained at each position is set to bea surface roughness R_(b) (nm) of the back surface.

Young’s Modulus of Magnetic Tape in Longitudinal Direction

A Young’s modulus of the magnetic tape MT in the longitudinal directionis preferably 8.0 GPa or less, more preferably 7.9 GPa or less, stillmore preferably 7.5 GPa or less, and particularly preferably 7.1 GPa orless. When the Young’s modulus of the magnetic tape MT in thelongitudinal direction is 8.0 GPa or less, the degree of expansion andcontraction of the magnetic tape MT due to an external force furtherincreases, and thus it is easier to adjust the width of the magnetictape MT by adjusting the tension. Therefore, it is possible to moreappropriately minimize off-track errors, and it is possible to moreaccurately reproduce data recorded in the magnetic tape MT.

The Young’s modulus of the magnetic tape MT in the longitudinaldirection is a value indicating a lower likelihood of expansion andcontraction of the magnetic tape MT in the longitudinal direction due toan external force, and when this value is larger, the magnetic tape MTis less likely to expand and contract in the longitudinal direction dueto an external force, and when this value is smaller, the magnetic tapeMT is more likely to expand and contract in the longitudinal directiondue to an external force.

Here, the Young’s modulus of the magnetic tape MT in the longitudinaldirection is a value related to the magnetic tape MT in the longitudinaldirection, but it also correlates with a lower likelihood of expansionand contraction of the magnetic tape MT in the width direction. That is,when this value is larger, the magnetic tape MT is less likely to expandand contract in the width direction due to an external force, and whenthis value is smaller, the magnetic tape MT is more likely to expand andcontract in the width direction due to an external force. Therefore, inconsideration of tension adjustment, a smaller Young’s modulus of themagnetic tape MT in the longitudinal direction is advantageous.

A tensile strength tester (AG-100D manufactured by Shimadzu Corporation)is used to measure the Young’s modulus. In a case where it is desired tomeasure the Young’s modulus of the tape in the longitudinal direction,the tape is cut to a length of 180 mm to prepare a measurement sample. Ajig that can fix the width (½ inch) of the tape is attached to thetensile strength tester, and the top and bottom of the tape width arefixed. The distance (the length of the tape between chucks) is 100 mm.After the tape sample is chucked, stress is gradually applied in thedirection in which the sample is pulled. A tensile speed is set to 0.1mm/min. The Young’s modulus is calculated using the following formulafrom the change in the stress and the amount of elongation in this case.

E  (N/m²)  =  ((ΔN/S / (Δx/L))  ×  10⁶

-   ΔN: Change in stress (N)-   S: Cross-sectional area of test piece (mm²)-   Δx: Amount of elongation (mm)-   L: Distance between gripping jigs (mm)

The range of stress is set to be from 0.5 N to 1.0 N, and a change instress (ΔN) and the amount of elongation (Δx) at this time are used inthe calculation. Note that the measurement of the Young’s modulus isperformed under an environment of 25° C. and 50% RH ± 5% RH. Young’sModulus of Substrate in Longitudinal Direction

A Young’s modulus of the substrate 41 in the longitudinal direction ispreferably 7.5 GPa or less, more preferably 7.4 GPa or less, still morepreferably 7.0 GPa or less, and particularly preferably 6.6 GPa or less.When the Young’s modulus of the substrate 41 in the longitudinaldirection is 7.5 Gpa or less, the degree of expansion and contraction ofthe magnetic tape MT due to an external force further increases, andthus it is easier to adjust the width of the magnetic tape MT byadjusting the tension. Therefore, it is possible to more appropriatelyminimize off-track errors, and it is possible to more accuratelyreproduce data recorded in the magnetic tape MT.

The Young’s modulus of the substrate 41 in the longitudinal direction isobtained as follows. First, the underlayer 42, the magnetic layer 43 andthe back layer 44 are removed from the magnetic tape MT to obtain thesubstrate 41. The Young’s modulus of the substrate 41 in thelongitudinal direction is obtained using the substrate 41 in the sameprocedure as in the above Young’s modulus of the magnetic tape MT in thelongitudinal direction.

The thickness of the substrate 41 occupies more than half of thethickness of the entire magnetic tape MT. Therefore, the Young’s modulusof the substrate 41 in the longitudinal direction correlates with alower likelihood of expansion and contraction of the magnetic tape MTdue to an external force, and when this value is larger, the magnetictape MT is less likely to expand and contract in the width direction dueto an external force, and when this value is smaller, the magnetic tapeMT is more likely to expand and contract in the width direction due toan external force.

Here, the Young’s modulus of the substrate 41 in the longitudinaldirection is a value related to the magnetic tape MT in the longitudinaldirection, and but it also correlates with a lower likelihood ofexpansion and contraction of the magnetic tape MT in the widthdirection. That is, when this value is larger, the magnetic tape MT isless likely to expand and contract in the width direction due to anexternal force, and when this value is smaller, the magnetic tape MT ismore likely to expand and contract in the width direction due to anexternal force. Therefore, in consideration of tension adjustment, asmaller Young’s modulus of the substrate 41 in the longitudinaldirection is advantageous.

Height Range ΔH, Gradient Range ΔA

A height range ΔH (see FIG. 16 ) obtained from statistical information(distribution) of the height of an uneven shape on the surface of themagnetic layer 43 is 4.00 nm ≤ΔH ≤10.00 nm, and preferably 4.00 nm ≤ΔH≤8.50 nm. When the height range ΔH is ΔH < 4.00 nm, the magnetic headsticks to the magnetic tape MT, and thus it becomes difficult for themagnetic tape MT to run. On the other hand, when the height range ΔH is10.00 nm < ΔH, an electromagnetic conversion characteristic (forexample, SNR) deteriorates due to a spacing loss.

A gradient range ΔA (see FIG. 16 ) obtained from statistical information(distribution) of the gradient of an uneven shape on the surface of themagnetic layer 43 is 2.50 degrees ≤ΔA, and preferably 2.50 degrees ≤ΔA <5.00 degrees. When the gradient range ΔA is ΔA < 2.50 degrees, arelative friction increases, and thus running stability of the magnetictape MT decreases. On the other hand, when the gradient range ΔA is 5.00degrees < ΔA, the gradient of a protrusion on the surface of themagnetic layer 43 becomes excessively steep, and the protrusion isscraped when the magnetic tape MT is running, so that powder falls off.

A method of calculating the height range ΔH and the gradient range ΔAwill be described in the following order.

-   (1) Surface profile measurement (AFM)-   (2) Calculation of relative height at each point-   (3) Calculation of gradient at each point-   (4) Statistical processing of data of height and gradient-   (5) Calculation of height range ΔH-   (6) Calculation of gradient range ΔA

Surface Profile Measurement (AFM)

By measuring a two-dimensional surface profile of the surface (magneticsurface) of the magnetic layer 43 of the magnetic tape MT, a numericaldata matrix of a height ζ(L,W) is obtained from a two-dimensionalsurface profile image after a filter action. Note that measurementconditions are as follows.

-   Measurement device: AFM (device name: Nanoscope Dimension 3100    manufactured by Digital Instruments Corporation)-   Measurement range: 40 µm × 40 µm-   Number of measurement points: 512 points × 512 points-   Scan rate: 1 Hz-   Filter condition: [Flatten] order 2    -   [Plane Fit] order 3, XY

FIG. 8A is a diagram illustrating an example of a two-dimensionalsurface profile image after a filter action. FIG. 8B is a diagramillustrating an example of a numerical data matrix of a height ζ(L,W) ateach point (L,W). The coordinate L indicates a coordinate in thelongitudinal direction of the magnetic tape MT, and the coordinate Windicates a coordinate in the width direction of the magnetic tape MT. Aheight ζ(L,W) at each point (L,W) is written in each cell of a numericaldata matrix. In the example illustrated in FIG. 8B, for example, aheight ζ(1,3) at a measurement point (1,3) is “0.50”. The number ofpieces of numerical data (that is, height ζ(L,W)) is a total of 512 ×512 = 262,144.

Calculation of Relative Height at each Point

A relative height Z(L,W) at each point (L,W) (hereinafter, referred tosimply as a "height Z(L,W)^(,,)) is calculated from the numerical datamatrix of a height ζ(L,W) to obtain a numerical data matrix of a heightZ(L,W). The height Z(L,W) at each point (L,W) is obtained specificallyas follows. That is, an average value is obtained by simply averaging(taking an arithmetic mean of) all of the heights ζ(L,W) and is set tobe an average center height ζ_(ave). Then, the height ζ(L,W) at eachpoint (L,W) is converted into a relative height based on the averagecenter height ζ_(ave) to obtain a height Z(L,W) at each point (L,W). Aformula representing a method of calculating the height Z(L,W) is asfollows. FIG. 9 is a diagram illustrating an example of a numerical datamatrix of a height Z(L,W).

$\zeta_{\text{ave}}\,\text{=}\,\,\frac{\sum\limits_{\text{w=1}}^{\text{512}}{\sum\limits_{\text{L=1}}^{\text{512}}{\,\,\,\,\,\zeta\text{(L,W)}}}}{\text{512×512}}$

Z(L, W)  = ζ(L,W) - ζ_(ave)

Calculation of Gradient at each Point

FIG. 10 is a diagram illustrating a method of calculating gradientsG_(L)(L,W) and Gw(L,W) at each point (L,W). Here, the gradientG_(L)(L,W) indicates a gradient in the longitudinal direction of themagnetic tape MT, and the gradient Gw(L,W) indicates a gradient in thewidth direction of the magnetic tape MT.

By calculating the gradients G_(L)(L,W) and G_(W)(L,W) in two directionsat each point (L,W) from a numerical data matrix of a height ζ(L,W), anumerical data matrix of each of the gradients G_(L)(L,W) and G_(W)(L,W)is obtained. FIG. 11A is a diagram illustrating an example of thenumerical data matrix of the gradient G_(L)(L,W). FIG. 11B is a diagramillustrating an example of the numerical data matrix of the gradientGw(L,W).

The gradient G_(L)(L,W) is calculated as follows. The gradientG_(L)(L,W) is calculated using a height ζ(L,W) at a certain point (L,W)and a height ζ(L+1,W) at a point (L+1,W) adjacent to the point (L,W) inthe longitudinal direction of the magnetic tape MT. As illustrated inFIG. 10 , for example, a gradient G_(L)(2,2) is calculated using aheight ζ(2,2) (= 0.30) at a point (2,2) and a height ζ(3,2) (= 0.10) ata point (3,2).

The gradient Gw(L,W) is calculated as follows. The gradient Gw(L,W) iscalculated using a height ζ(L,W) at a certain point (L,W) and a heightζ(L,W+1) at a point (L,W+1) adjacent to the point (L,W) in the widthdirection of the magnetic tape MT. As illustrated in FIG. 10 , forexample, the gradient Gw(2,2) is calculated using a height ζ(2,2) (=0.30) at a point (2,2) and a height ζ(2,3) (= 0.10) at a point (2,3).

As described above, the “adjacent point” used at the time of calculatingG_(L)(L,W) at each point (L,W) is a point (L+1,W). An adjacent point inthe opposite direction, that is, a point (L-1, W) should not be used.Similarly, the “adjacent point” used at the time of calculating Gw(L,W)at each point (L,W) is a point (L,W+1). An adjacent point in theopposite direction, that is, a point (L,W-1) should not be used.

As illustrated in FIG. 10 , a gradient G_(L)(512,W) cannot be calculatedat each point (512,W) of L = 512 (that is, the rightmost column in FIG.10 ) of the numerical data matrix. For this reason, as illustrated inFIG. 11A, each point (512,W) of L = 512 does not have a value in thenumerical data matrix of the gradient G_(L)(L,W). On the other hand, asillustrated in FIG. 10 , a gradient Gw(L,512) cannot be calculated ateach point (L,512) of W = 512 (that is, the lowermost row in FIG. 10 )of the numerical data matrix. For this reason, as illustrated in FIG.11B, each point (L,512) of W = 512 does not have a value in thenumerical data matrix of the gradient Gw(L,W).

However, as illustrated in FIG. 10 , both a gradient G_(L)(512,512) anda gradient G_(W)(512,512) cannot be calculated at points (L,W) of L =512, W = 512 (the rightmost and lowermost column and the lowermost row)of the numerical data matrix, and thus a point (512,512) does not haveboth the gradient G_(L)(512,512) and the gradient Gw(512,512).

FIG. 12A is a diagram illustrating a method of calculating a gradientG_(L)(L,W). FIG. 12B is a diagram illustrating a method of calculating agradient Gw(L,W). A formula representing a method of calculating thegradients G_(L)(L,W) and G_(w)(L,W) is as follows.

$\text{G}_{\text{L}}\left( \text{L,W} \right)\lbrack{^\circ}\rbrack = \tan^{- 1}\left( \frac{\left| {\zeta\left( \text{L+1,W} \right) - \zeta\left( \text{L,W} \right)} \right|}{78.125} \right)$

$\text{G}_{\text{W}}\left( \text{L,W} \right)\lbrack{^\circ}\rbrack = \tan^{- 1}\left( \frac{\left| {\zeta\left( {\text{L,W+}1} \right) - \zeta\left( \text{L,W} \right)} \right|}{78.125} \right)$

Statistical Processing of Data of Height and Gradient

FIGS. 13, 14, and 15 are diagrams illustrating statistical processing ofdata of the height Z(L,W), the gradient G_(L)(L,W), and the gradientGw(L,W). A numerical data matrix of the height Z(L,W) and the gradientG_(L)(L,W) which are obtained as described above is organized, and atable (see FIG. 13 ) representing a relationship between the heightZ(L,W) and the gradient G_(L)(L,W) is created. However, since there isno gradient G_(L)(512,W), a total number of pieces of data in thecreated table is 511x512 = 261,632.

In addition, a numerical data matrix of the height Z(L,W) and thegradient G_(W)(L,W) is organized, and a table (see FIG. 14 )representing a relationship between the height Z(L,W) and the gradientG_(W)(L,W) is created. However, since there is no Gw(L,512), a totalnumber of pieces of data in the created table is 512×511 = 261,632.

All of the pieces of data of the two created tables (that is, 523,264 =261,632 + 261,632) are aggregated, and a numerical data matrix of thenumber of pieces of data M(H,A) is created as illustrated in FIG. 15 .When numerical values of cells of the numerical data matrix of thenumber of pieces of data M(H,A) are added, a total number of pieces ofdata is 523,264.

In FIG. 15 , the range of a height Z(L,W) and its representative value Hare described alongside the column of the numerical data matrix of thenumber of pieces of data M(H, A). In addition, the range of a gradientG(L,W) and its representative value A are described alongside the row ofthe numerical data matrix of the number of pieces of data M(H, A). Notethat, in a case where the gradient G_(L)(L,W) and the gradientG_(W)(L,W) are not particularly distinguished from each other, thegradient G_(L)(L,W) and the gradient G_(W)(L,W) will be collectivelyreferred to as a gradient G(L,W).

Numerical values (see FIG. 15 ) of cells of the numerical data matrix ofthe number of pieces of data M(H,A) represent the number of pieces ofdata M(H,A) corresponding to the range of a specified height Z(L,W) andcorresponding to the range of a specified gradient G(L,W) (specifically,the gradient G_(L)(L,W) or the gradient G_(W)(L,W)). For example, datain a first row of a table of Z(L,W) vs.G_(L)(L,W) is counted in a (H,A)= (0.0,0.00) cell in M(H,A). In addition, 261630th data in a table ofZ(L,W) vs.G_(W)(L,W) is counted in a (H,A) = (-0.5,0.00) cell in M(H,A).

When the numerical data matrix M(H, A) (see FIG. 15 ) obtained asdescribed above is drawn as a distribution map on a horizontal axis Aand a vertical axis H, FIG. 16 is obtained.

Calculation of Height Range ΔH

FIGS. 17 and 18 are diagrams illustrating a method of calculating aheight range ΔH. When the height range ΔH is calculated, only components(cells) in the range of 0 ≤H, 0.00 ≤A ≤ 1.20 in the numerical datamatrix of the number of pieces of data M(H,A) are used. Regarding theheight H, only components in the range of 0 ≤H are used because only aconvex portion on a magnetic surface is taken into consideration. Thatis, this is because it is considered that a concave portion on themagnetic surface does not affect electromagnetic conversioncharacteristics and friction. On the other hand, regarding the gradientA, only components in the range of 0.00 ≤ A ≤ 1.20 are used because itis considered that it is sufficient to define a rough outline ofdistribution (see FIG. 16 ) when even this range is used in thecalculation.

As illustrated in FIG. 17 , an average value in each row (height H) ofthe numerical data matrix of the number of pieces of data M(H,A) is setto be M_(ave)(H), and calculation is sequentially performed from anaverage value M_(ave)(0) to an average value M_(ave)(40.0). However, inthe calculation of the average value M_(ave)(H), regarding a column(angle A), only components of columns (angle A) in the range of 0.00 ≤ A≤ 1.20 are used.

A height H when the average value M_(ave)(H) falls below a thresholdvalue (where, the threshold value is set to “3”) for the first time isset to be a height H_(high), and an average value M_(ave)(H) at thattime is set to be an average value M_(ave)(H_(high)). Further, oneheight H prior to the height is set to be a height H_(low), and anaverage value M_(ave)(H) at that time is set to be an average valueM_(ave)(H_(low)). When the threshold value is set to “1” or “2”,reproducibility deteriorates. That is, an accidental factor has a greatinfluence. Thus, “3” which is the least frequency at whichreproducibility can be secured is set to be a threshold value.

In the example of FIG. 17 , the height H_(high), the average valueM_(ave)(H_(high)), the height H_(low), and the average valueM_(ave)(H_(low)) are as follows.

H_(high=)11.5, M_(ave)(H_(high))=2.4

H_(low)=11.0,M_(ave)(H_(low))=4.2

As illustrated in FIG. 18 , a height H is calculated when M_(ave)(H) =threshold value = 3 by using the four values, and is defined as a heightrange ΔH. Note that, when the height H is calculated, a linearapproximation between two points is used.

Calculation of Gradient Range ΔA

FIGS. 19 and 20 are diagrams illustrating a method of calculating agradient range ΔA. When the gradient range ΔA is calculated, onlycomponents (cells) in the range of 0 ≤ H ≤ ΔH, 0.00 ≤ A ≤ 16.00 in thenumerical data matrix of the number of pieces of data M(H,A) are used.Regarding ΔH, the value obtained in the above-described “(5) Calculationof height range ΔH” is used. Regarding the gradient A, only componentsin the range of 0.00 ≤ A ≤ 16.00 are used because the gradient A isgenerally in the range of 0.00 ≤ A ≤ 16.00, and it is considered that itis sufficient to use even this range for the calculation.

As illustrated in FIG. 19 , an average value of pieces of data M(H,A) ineach column (angle A) of the numerical data matrix of M(H,A) is set tobe M_(ave)(A), and calculation is sequentially performed from an averagevalue M_(ave)(0) to an average value M_(ave)(16.00). However, in thecalculation of the average value M_(ave)(A), regarding a row (height H),only components of rows (height H) in the range of 0.00 ≤ H ≤ ΔH areused.

In a case where the height range ΔH is not a multiple of 0.5, componentsof rows (height H) in the range up to the height H_(low) which are usedin the calculation of the height range ΔH are used to calculate theaverage value M_(ave)(A). For example, as illustrated in FIG. 19 , in acase where the height range ΔH is in a range between 11.0 and 11.5,components of rows (height H) in the range of 0.00 ≤ H ≤ 11.0 are used.

A when the average value M_(ave)(A) falls below a threshold value(where, the threshold value is set to “3”) for the first time is set tobe A_(high), and an average value M_(ave)(A) at that time is set to beaverage value M_(ave)(A_(high)). Further, one angle A prior to the angleis set to be an angle A_(low), and an average value M_(ave)(A) at thattime is set to be an average value M_(ave)(A_(low)). The reason why thethreshold value of the average value M_(ave)(A) is set to “3” is thesame as the reason why the threshold value of the average valueM_(ave)(H) is set to “3”.

In the example of FIG. 19 , A_(high), M_(ave)(A_(high)), A_(low), andM_(ave)(A_(low)) are as follows.

A_(high)=3.36,M_(ave)(A_(high))=2.9

A_(low) = 3.28, M_(ave)(A_(low)) = 3.2

As illustrated in FIG. 20 , an angle A is calculated when M_(ave)(A) =threshold value = 3 by using the four values, and is defined as agradient range ΔA. Note that, when the angle A is calculated, a linearapproximation between two points is used.

Amount of Oozing of Lubricant

The amount of oozing (oozing area) of a lubricant per unit region of12.5 µm × 9.3 µm on the surface of the magnetic layer 43 in vacuum is3.0 µm² or more and 6.5 µm² or less, and preferably 3.5 µm² or more and6.5 µm² or less. The amount of oozing of the lubricant on the surface ofthe magnetic layer 43 in vacuum corresponds to the amount of lubricantthat can be supplied when the magnetic tape MT is running. When theamount of oozing of the lubricant (area) is less than 3.0 µm², theamount of lubricant on the surface of the magnetic layer 43 isexcessively small, and thus a dynamic friction coefficient increaseswhen recording or reproducing is repeatedly performed. On the otherhand, when the amount of oozing of the lubricant (area) exceeds 6.5 µm²,the amount of lubricant on the surface of the magnetic layer 43 isexcessively large, and thus a surface portion of the magnetic layer 43is plasticized due to the lubricant, and the hardness of the surface ofthe magnetic layer 43 deteriorates. Thus, the head is in excessivelyclose contact with the magnetic tape MT when the magnetic tape MT isrunning, and thus a dynamic friction coefficient increases. Hereinafter,the amount of oozing of a lubricant per unit region 12.5 µm × 9.3 µm onthe surface of the magnetic layer 43 in vacuum may be referred to simplyas “the amount of oozing of a lubricant”.

The amount of oozing of a lubricant (area) is obtained as follows.First, the magnetic tape MT is cut by 5 cm, stuck to a slide glass, andinstalled in an MSP-1S type magnetron sputtering device manufactured byVacuum Device Co., Ltd. The magnetic layer 43 is attached with thesurface thereof facing up. Next, pressure in the sputtering device isreduced to 4 Pa. Thereafter, a target (ϕ51 mm, thickness of 0.1 mm,material: Pt—Pd) manufactured by Vacuum Device Co., Ltd. is sputteredfor 6 seconds to form a Pt—Pd alloy on the surface (magnetic surface) ofthe magnetic layer 43. A sputtering film is unlikely to be formed at alocation where a lubricant is present, whereas a sputtering film islikely to be formed at a location where a lubricant is not present. Forthis reason, the sputtering film is unevenly distributed in a portion inwhich a lubricant is present and a portion in which a lubricant is notpresent. Next, the surface of the magnetic layer 43 is observed with ascanning electron microscope (SEM) under the following conditions toobtain a Tif file (1260 × 960 pixels) of an SEM image (black and whiteshading image) of the observed surface. Note that, in the SEM image, apart that looks black corresponds to a part in which a lubricant ispresent.

-   Device: Hitachi High-Technologies Corporation, S-4800-   Acceleration voltage: 5 kV-   Magnification: 10000x

Next, the amount of oozing of a lubricant (area) is obtained as followsfrom an SEM image (Tif file) of the obtained unit region of 12.5 µm ×9.3 µm by using image analysis software (ImageJ). First, scaling of theobtained SEM image is performed (scaling setting conditions: distance =504, known = 5, pixel = 1, unit = um (micrometer)). Next, the scaled SEMimage (black and white shading image) is divided into 256 gradations,and the SEM image is binarized with 70 gradations as a threshold value.Specifically, when a pixel has 70 gradations or less, the pixel is“black”, and when a pixel exceeds 70 gradations, the pixel is “white”.FIG. 21A illustrates an example of the binarized SEM image. A partdisplayed in “black” by binarization corresponds to a part in which alubricant is present on the surface of the magnetic layer 43.

Next, a total area of dots (black portion) having an area of 0.02 µm² ormore is obtained from the binarized SEM image by Analyze Particles ofImageJ (particle analysis). Here, the reason why a dot having an arealess than 0.02 µm² is excluded is because there is a possibility that adot having an area less than 0.02 µm² will be a particle such as carbonblack, and even when a dot having an area less than 0.02 µm² is alubricant, it has little effect on running performance. FIG. 21Billustrates an example of an outline image of a dot having an area of0.02 µm² or more.

Details of setting of Analyze Particles are as follows.

-   Size: 0.02-Infinity-   Show: Outlines

The above-described calculation of a total area is performed at threelocations randomly selected from a slide glass, and calculation resultsare simply averaged (arithmetic mean) to obtain the amount of oozing ofa lubricant.

Friction Coefficient

A friction coefficient ratio (µ_(B)/µ_(A)) between a dynamic frictioncoefficient µ_(B) obtained after full-scale recording/full-scalereproduction is performed twice and a dynamic friction coefficient µ_(A)before the full-scale recording/full-scale reproduction is performed ispreferably less than 2.0, more preferably 1.5 or less, still morepreferably 1.3 or less, and particularly preferably 1.1 or less. Whenthe friction coefficient ratio (µ_(B)/µ_(A)) is less than 2.0, it ispossible to suppress the occurrence of defective data writing andreading due to sticking and running instability in the thirdrecording/reproducing and the subsequent recording/reproducingprocesses. Here, the “full-scale recording/full-scale reproduction”means that data having a maximum uncompressed capacity (for example, 6TB in the case of LTO7) of a cartridge is continuously written, and thenall of the written information is reproduced. For “full-scalerecording/full-scale reproduction”, it is assumed that a drivecompatible with the magnetic tape MT is used as a magnetic head. Inaddition, it is assumed that “full-scale recording/full-scalereproduction” is performed at room temperature.

The friction coefficient ratio (µ_(B)/µ_(A)) is obtained as follows.First, after full-scale recording/full-scale reproduction is performedtwice on the magnetic tape MT, the magnetic tape MT is unwound from thecartridge 10, and a portion 2 m from a connection portion between aleader tape portion and the magnetic tape MT is set to be a “portionbefore full-scale recording/full-scale reproduction is performed twice”(hereinafter, referred to as a “non-recording/reproducing portion”). Inaddition, a portion 50 m from the connection portion between the readertape portion and the magnetic tape MT is set to be a “portion on whichfull-scale recording/full-scale reproduction has been performed twice”(hereinafter, referred to as a “recording/reproducing portion”). Next,as illustrated in FIG. 22A, the magnetic tape MT of thenon-recording/reproducing portion is placed on two columnar guide rolls73A and 73B so that the magnetic surface thereof is in contact with theguide rolls 73A and 73B, the guide rolls having a diameter of 1 inch andbeing disposed separately and in parallel with each other. The two guiderolls 73A and 73B are fixed to a hard plate-shaped member 76, whereby apositional relationship therebetween is fixed.

Next, the magnetic tape MT is brought into contact with a head block(for recording and reproduction) 74 mounted on an LTO5 drive so that themagnetic surface of the magnetic tape MT is in contact with the headblock and a holding angle θ1 (°) = 5.6 degrees. The head block 74 isdisposed substantially between the guide rolls 73A and 73B. Although thehead block 74 is attached to be movable to the plate-shaped member 76 soas to be able to change the holding angle θ1, the position of the headblock is fixed to the plate-shaped member 76 when the holding angle θ1(°) is set to 5.6 degrees, and thus a positional relationship betweenthe guide rolls 73A and 73B and the head block 74 is also fixed.

One end portion of the magnetic tape MT is connected to a movable straingauge 71 via a jig 72. The magnetic tape MT is fixed to the jig 72 asillustrated in FIG. 22B. A weight 75 is connected to the other end ofthe magnetic tape MT. A tension (T₀ [N]) of 0.6 N is applied in thelongitudinal direction of the magnetic tape MT by the weight 75. Themovable strain gauge 71 is fixed onto a stand 77. A positionalrelationship between the stand 77 and the plate-shaped member 76 is alsofixed, and thus a positional relationship between the guide rolls 73Aand 73B, the head block 74, and the movable strain gauge 71 is fixed.

The movable strain gauge 71 slides the magnetic tape MT 60 mm on thehead block 74 (outward path) so that the magnetic tape MT is directedtoward the movable strain gauge 71 at 10 mm/s, and slides the magnetictape MT 60 mm so as to be away from the movable strain gauge (returnpath). An output value (voltage) of the movable strain gauge 71 at thetime of the sliding is converted into a load T[N] on the basis of alinear relationship between an output value acquired in advance and aload (which will be described later). T [N] is acquired 13 times fromthe start of the 60 mm sliding to the stop of the sliding, and 11 valuesof T [N] except for the first and last two values are simply averaged toobtain Tave [N]. Thereafter, a dynamic friction coefficient µ_(A) isobtained by the following formula.

$\mu_{\text{A}} = \frac{1}{\left( {\theta_{1}\left\lbrack {}^{\circ} \right\rbrack} \right) \times \left( {\pi/180} \right)} \times \ln\left( \frac{\text{T}_{\text{ave}}\left\lbrack \text{N} \right\rbrack}{\text{T}_{0}\left\lbrack \text{N} \right\rbrack} \right)$

The linear relationship is obtained as follows. That is, an output value(voltage) of the movable strain gauge 71 is obtained for each of a casewhere a load of 0.5 N is applied to the movable strain gauge 71 and acase where a load of 1.0 N is applied to the movable strain gauge 71. Alinear relationship between an output value and a load is obtained fromthe obtained two output values and the two loads. The output value(voltage) of the movable strain gauge 71 at the time of the sliding isconverted into T [N] as described above using the linear relationship.

Next, a dynamic friction coefficient µ_(B) is obtained from the magnetictape MT of the recording/reproducing portion according to the sameprocedure as when the dynamic friction coefficient µ_(A) is obtainedfrom the magnetic tape MT of the non-recording/reproducing portion.

A friction coefficient ratio (µ_(B)/µ_(A)) is calculated from thedynamic friction coefficient µ_(A) and the dynamic friction coefficientµ_(B) obtained as described above.

4 Method of Manufacturing Magnetic Tape

Next, an example of a method of manufacturing a magnetic tape MT havingthe above-described configuration will be described.

Preparation Process of Coating Material

First, an underlayer forming coating material is prepared by kneadingand dispersing a non-magnetic powder, a binding agent, and the like in asolvent. Next, a magnetic layer forming coating material is prepared bykneading and dispersing a magnetic powder, a binding agent, and the likein a solvent. For example, the following solvents, a dispersion device,and a kneading device can be used to prepare the magnetic layer formingcoating material and the underlayer forming coating material.

Examples of solvents used to prepare the above-described coatingmaterials include ketone-based solvents such as acetone, methyl ethylketone, methyl isobutyl ketone and cyclohexanone, alcohol-based solventssuch as methanol, ethanol and propanol, ester-based solvents such asmethyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyllactate and ethylene glycol acetate, ether-based solvents such asdiethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran anddioxane, aromatic hydrocarbon-based solvents such as benzene, tolueneand xylene, halogenated hydrocarbon-based solvents such as methylenechloride, ethylene chloride, carbon tetrachloride, chloroform, andchlorobenzene, and the like. These may be used alone or mixedappropriately.

As a kneading device used to prepare the above-described coatingmaterial, for example, kneading devices such as a continuous twin-screwkneader, a continuous twin-screw kneader that can perform dilution inmultiple stages, a kneader, a pressure kneader, and a roll kneader canbe used, but the present disclosure is not limited to these devices. Inaddition, as the dispersion device used to prepare the above-describedcoating materials, for example, dispersion devices such as a roll mill,a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill,a pin mill, a tower mill, a pearl mill (for example, a “DCP mill”manufactured by Erich), a homogenizer, and an ultrasonic disperser canbe used, but the present invention is not particularly limited to thesedevices.

Application Process

Next, an underlayer forming coating material is applied to one mainsurface of the substrate 41 and dried to form the underlayer 42.Subsequently, a magnetic layer forming coating material is applied ontothe underlayer 42 and dried to form the magnetic layer 43 on theunderlayer 42. Note that, at the time of the drying, a magnetic powderis magnetically oriented in the thickness direction of the substrate 41by, for example, a solenoid coil. In addition, at the time of thedrying, the magnetic powder may be magnetically oriented in a runningdirection (longitudinal direction) of the substrate 41 by, for example,a solenoid coil, and then magnetically oriented in the thicknessdirection of the substrate 41. By performing a process of temporarilyorienting the magnetic powder in the longitudinal direction in thismanner, the degree of vertical orientation of the magnetic powder (thatis, the squareness ratio S1) can be further improved. After the magneticlayer 43 is formed, the back layer 44 is formed on the other mainsurface of the substrate 41. Thereby, the magnetic tape MT is obtained.

The squareness ratios S1 and S2 are set to desired values by adjusting,for example, the strength of a magnetic field applied to a coating filmof the magnetic layer forming coating material, the concentration ofsolid content in the magnetic layer forming coating material, and dryingconditions (a drying temperature and a drying time) of the coating filmof the magnetic layer forming coating material. The strength of themagnetic field applied to the coating film is preferably 2 times or moreand 3 times or less a coercive force of the magnetic powder. In order tofurther increase the squareness ratio S1 (that is, to further lower thesquareness ratio S2), it is preferable to improve the dispersed state ofthe magnetic powder in the magnetic layer forming coating material.Further, in order to further increase the squareness ratio S1, it isalso effective to magnetize the magnetic powder at a stage beforemagnetic layer forming coating material is injected into an orientationdevice for magnetically orienting the magnetic powder. Note that theabove-mentioned method of adjusting the squareness ratios S1 and S2 maybe used alone or in combination of two or more.

Calendering Process

Next, the obtained magnetic tape MT is subjected to calendering tosmooth the surface of the magnetic layer 43.

A height range ΔH and a gradient range ΔA can be set to specified valuesby adjusting, for example, at least one of (1) the size and content ofan additive (particles) to be mixed in the magnetic layer formingcoating material, (2) the size and content of a non-magnetic powder tobe mixed in the underlayer forming coating material, and (3) calenderingconditions (temperature and pressure). The additive to be mixed in themagnetic layer forming coating material is, for example, an abrasivesuch as α-alumina. The non-magnetic powder to be mixed in the underlayerforming coating material is, for example, needle-like iron oxide powderor the like.

As the size of the additive to be mixed in the magnetic layer formingcoating material becomes larger, there is a tendency for the heightrange ΔH and the gradient range ΔA to increase. As the content of theadditive to be mixed in the magnetic layer forming coating materialincreases, there is a tendency for the height range ΔH and the gradientrange ΔA to increase. As the size of the non-magnetic powder to be mixedin the underlayer forming coating material becomes larger, there is atendency for the height range ΔH and the gradient range ΔA to increase.As the content of the non-magnetic powder to be mixed in the underlayerforming coating material increases, there is a tendency for the heightrange ΔH and the gradient range ΔA to increase. As the temperature ofthe calendering increases, there is a tendency for the height range ΔHand the gradient range ΔA to decrease. As the pressure of thecalendering increases, there is a tendency for the height range ΔH andthe gradient range ΔA to decrease.

The amount of oozing of a lubricant can be set to a specified value byadjusting, for example, conditions of calendering (temperature andpressure). In order to set the amount of oozing of a lubricant to 3.0µm² or more and 6.5 µm² or less, the temperature of the calendering ispreferably in the range of 80° C. or more and 130° C. or less, and thepressure is preferably in the range of 150 kg/cm or more and 350 kg/cmor less. Note that, as the temperature of the calendering increases,there is a tendency for the amount of oozing of a lubricant to decrease.In addition, as the pressure of the calendering increases, there is atendency for the amount of oozing of a lubricant to decrease. Here, thetemperature of the calendering is the surface temperature of a roll thatpresses the surface of the magnetic layer 43 during the calendering.

The amount of oozing of a lubricant can also be set to a specified valueby adjusting, for example, a drying temperature of the coating film ofthe magnetic layer forming coating material. In order to set the amountof oozing of a lubricant to 3.0 µm² or more and 6.5 µm² or less, thedrying temperature is preferably in the range of 60° C. or more and 120°C. or less, and the drying time is preferably in the range of 5 secondsor more and 30 seconds or less. Note that, as the drying temperatureincreases, there is a tendency for the amount of oozing of a lubricantto increase. In addition, as the drying time increases, there is atendency for the amount of oozing of a lubricant to increase.

Cutting Process

Next, the magnetic tape MT is cut to a predetermined width (for example,a width of ½ inches). In this manner, the magnetic tape MT is obtained.

Demagnetization Process and Servo Pattern Writing Process

Next, a servo pattern may be written on the magnetic tape MT afterperforming demagnetization of the magnetic tape MT as necessary.

5 Effects

As described above, in the magnetic tape MT according to an embodiment,in addition to the height of the uneven shape of the surface of themagnetic layer 43, the inclination of the uneven shape of the surface ofthe magnetic layer 43 is specified. Specifically, in addition to settingthe height range ΔH obtained from statistical information (distribution)of the height of the uneven shape of the surface of the magnetic layer43 to be in a range of 4.0 nm ≤ ΔH ≤ 10 nm, the gradient range ΔAobtained from statistical information (distribution) of the gradient ofthe uneven shape of the surface of the magnetic layer 43 is set to be ina range of 2.5 degrees ≤ ΔA. Thereby, it is possible to achieve bothexcellent recording/reproducing characteristics (electromagneticconversion characteristics) and excellent running stability (lowfriction).

6 Modification Examples Modification Example 1

In the above-described embodiment, a case where the magnetic tapecartridge is a 1-reel type cartridge 10 has been described, but themagnetic tape cartridge may be 2-reel type cartridge.

FIG. 23 is an exploded perspective view illustrating an example of aconfiguration of a 2-reel type cartridge 121. The cartridge 121 includesan upper half 102 made of a synthetic resin, a transparent window member123 fitted and fixed to a window portion 102 a opened on the uppersurface of the upper half 102, a reel holder 122 that is fixed to theinside of the upper half 102 to prevent reels 106 and 107 from floating,a lower half 105 that corresponds to the upper half 102, the reels 106and 107 that are accommodated in a space formed by combining the upperhalf 102 and the lower half 105, a magnetic tape MT1 that is woundaround the reels 106 and 107, a front lid 109 that closes a frontopening formed by combining the upper half 102 and the lower half 105,and a back lid 109A that protects the magnetic tape MT1 exposed on thefront opening.

The reel 106 includes a lower flange 106 b having a cylindrical hubportion 106 a around which the magnetic tape MT1 is wound in the centerthereof, an upper flange 106 c having substantially the same size as thelower flange 106 b, and a reel plate 111 sandwiched between the hubportion 106 a and the upper flange 106 c. The reel 107 has the sameconfiguration as the reel 106.

The window member 123 is provided with attachment holes 123 a forassembling the reel holder 122, which is a reel holding means forpreventing the reels from floating, at positions corresponding to thereels 106 and 107. The magnetic tape MT1 is the same as the magnetictape MT in a first embodiment.

Modification Example 2

In the above-described embodiment, in a case where a magnetic powdercontains hexagonal ferrite particle powder, an average particle size ofthe magnetic powder may be, for example, 13 nm or more and 22 nm orless, 13 nm or more and 19 nm or less, 13 nm or more and 18 nm or less,14 nm or more and 17 nm or less, or 14 nm or more and 16 nm or less.

In the above-described embodiment, in a case where a magnetic powdercontains hexagonal ferrite particle powder, average aspect ratio of themagnetic powder may be, for example, 1.0 or more and 3.0 or less, 1.5 ormore and 2.8, or less or 1.8 or more and 2.7 or less.

In the above-described embodiment, in a case where a magnetic powdercontains hexagonal ferrite particle powder, an average particle volumeof the magnetic powder may be, for example, 500 nm³ or more and 2500 nm³or less, 500 nm³ or more and 1600 nm³ or less, 500 nm³ or more and 1500nm³ or less, 600 nm³ or more and 1200 nm³ or less, or 600 nm³ or moreand 1000 nm³ or less.

In the above-described embodiment, in a case where a magnetic powdercontains ε-iron oxide particle powder, an average particle size of themagnetic powder may be, for example, 10 nm or more and 20 nm or less, 10nm or more and 18 nm or less, 10 nm or more and 16 nm or less, 10 nm ormore and 15 nm or less, or 10 nm or more and 14 nm or less.

In the above-described embodiment, in a case where a magnetic powdercontains ε-iron oxide particle powder, an average aspect ratio of themagnetic powder may be, for example, 1.0 or more and 3.0 or less, 1.0 ormore and 2.5 or less, 1.0 or more and 2.1 or less, or 1.0 or more and1.8 or less.

In the above-described embodiment, in a case where a magnetic powdercontains ε-iron oxide particle powder, an average particle volume of themagnetic powder may be, for example, 500 nm³ or more and 4000 nm³ orless, 500 nm³ or more and 3000 nm³ or less, 500 nm³ or more and 2000 nm³or less, 600 nm³ or more and 1600 nm³ or less, or 600 nm³ or more and1300 nm³ or less.

In the above-described embodiment, in a case where a magnetic powdercontains cobalt ferrite particle powder, an average particle size of themagnetic powder may be, for example, 8 nm or more and 20 nm or less, 8nm or more and 18 nm or less, 8 nm or more and 16 nm or less, 8 nm ormore and 13 nm or less, or 8 nm or more and 10 nm or less.

In the above-described embodiment, in a case where a magnetic powdercontains cobalt ferrite particle powder, an average aspect ratio of themagnetic powder may be, for example, 1.0 or more and 3.0 or less, 1.0 ormore and 2.5 or less, 1.0 or more and 2.1 or less, or 1.0 or more and1.8 or less.

In the above-described embodiment, in a case where a magnetic powdercontains cobalt ferrite particle powder, an average particle volume ofthe magnetic powder may be, for example, 500 nm³ or more and 8000 nm³ orless, 500 nm³ or more and 6000 nm³ or less, 500 nm³ or more and 4000 nm³or less, 600 nm³ or more and 2000 nm³ or less, or 600 nm³ or more and1000 nm³ or less.

EXAMPLES

Hereinafter, the present disclosure will be described below in detailwith reference to examples, but the present disclosure is not limited tothese examples.

In the following examples and comparative examples, an average aspectratio of a magnetic powder, an average particle volume of a magneticpowder, a height range ΔH, a gradient range ΔA, the amount of oozing ofa lubricant, an average thickness of a magnetic tape, an averagethickness of a magnetic layer, an average thickness of an underlayer, anaverage thickness of a back layer, a squareness ratio S1 of a magneticlayer in the vertical direction of a magnetic tape, and a squarenessratio S2 of a magnetic layer in the longitudinal direction of a magnetictape are values obtained by the measurement method described in theabove-described embodiment.

Further, in the following examples and comparative examples, a heightrange ΔH, a gradient range ΔA, and the amount of oozing of a lubricantare values measured by a magnetic tape (a magnetic tape having beensubjected to a calendering process) and obtained finally.

Example 1 Preparation Process of Magnetic Layer Forming Coating Material

A magnetic layer forming coating material is prepared as follows. First,a first composition having the following mixture was kneaded by anextruder. Next, the kneaded first composition and a second compositionhaving the following mixture were added to a stirring tank equipped witha disperser, and premixing was performed. Subsequently, sand mill mixingwas further performed and filtering was performed to prepare a magneticlayer forming coating material.

First composition

-   Barium ferrite (BaFe₁₂O₁₉) magnetic powder (hexagonal plate shape,    average aspect ratio of 3.2, average particle volume of 2500 nm³):    100 parts by mass-   Vinyl chloride resin (cyclohexanone solution of 30% by mass): 65    parts by mass (containing a solution)-   (Polymerization degree 300, Mn = 10000, containing OSO₃ K = 0.07    mmol/g, secondary OH = 0.3 mmol/g as a polar group)-   Aluminum oxide powder having a medium particle size: 7.5 parts by    mass (α—Al₂O₃, average particle size (D50) of 0.09 µm)

Second Composition

-   Vinyl chloride resin: 1.1 parts by mass-   (Resin solution: resin content of 30% by mass, cyclohexanone of 70%    by mass)-   n-butyl stearate: 2 parts by mass-   Methyl ethyl ketone: 121.3 parts by mass-   Toluene: 121.3 parts by mass-   Cyclohexanone: 60.7 parts by mass-   Carbon black: 2 parts by mass-   (Made by Tokai Carbon Co., Ltd., trade name: Seast TA)

Finally, polyisocyanate of 4 parts by mass (trade name: coronate Lmanufactured by Tosoh Corporation) as a curing agent and stearic acid of2 parts by mass as a lubricant were added to the magnetic layer formingcoating material prepared as described above.

Preparation Process of Underlayer Forming Coating Material

An underlayer forming coating material was prepared as follows. First, athird composition having the following mixture was kneaded by anextruder. Next, the kneaded third composition and a fourth compositionhaving the following mixture were added to a stirring tank equipped witha disperser, and premixing was performed. Subsequently, sand mill mixingwas further performed and filtering was performed to prepare anunderlayer forming coating material.

Third Composition

-   Needle-like iron oxide powder (non-magnetic powder) having a medium    particle size: 100 parts by mass-   (α—Fe₂O₃, average major axis length of 0.08 µm)-   Vinyl chloride resin: 55.6 parts by mass-   (Resin solution: resin content 30% by mass, cyclohexanone 70% by    mass)-   Carbon black: 10 parts by mass-   (average particle size of 20 nm)

Fourth Composition

-   Polyurethane resin UR8200 (manufactured by Toyo Boseki Kabushiki    Kaisha):-   18.5 parts by mass-   n-butyl stearate: 2 parts by mass-   Methyl ethyl ketone: 108.2 parts by mass-   Toluene: 108.2 parts by mass-   Cyclohexanone: 18.5 parts by mass

Finally, polyisocyanate of 4 parts by mass (trade name: coronate Lmanufactured by Tosoh Corporation) as a curing agent and stearic acid of2 parts by mass as a lubricant were added to the underlayer formingcoating material prepared as described above.

Preparation Process of back Layer Forming Coating Material

A back layer forming coating material was prepared as follows. Thefollowing raw materials were mixed in a stirring tank equipped with adisperser and filtered to prepare a back layer forming coating material.

-   Carbon black powder (average particle size (D50) 20 nm): 100 parts    by mass-   Polyester polyurethane: 100 parts by mass-   (Made by Nippon Polyurethane Industry Co., Ltd., trade name: N-2304)-   Methyl ethyl ketone: 500 parts by mass-   Toluene: 400 parts by mass-   Cyclohexanone: 100 parts by mass

Coating Process

An underlayer and a magnetic layer were formed on one main surface of along polyethylene naphthalate film (hereinafter, referred to as a “PENfilm”) having an average thickness of 3.6 µm, which is a non-magneticsupport, as follows by using the magnetic layer forming coating materialand the underlayer forming coating material which were prepared asdescribed above. First, an underlayer forming coating material wasapplied on one main surface of the PEN film and dried to form anunderlayer so that an average thickness thereof was set to 1.1 µm aftercalendering. Next, a magnetic layer forming coating material was appliedon the underlayer and dried to form a magnetic layer so that an averagethickness thereof was set to 85 nm after calendering. Note that, whenthe magnetic layer forming coating material was dried, the magneticpowder was magnetically oriented in the thickness direction of the filmby a solenoid coil. In addition, a squareness ratio S1 in the verticaldirection (thickness direction) of the magnetic tape was set to 65%, anda squareness ratio S2 in the longitudinal direction of the magnetic tapewas set to 38%. Subsequently, a back layer forming coating material wasapplied on the other main surface of the PEN film and dried to form aback layer so that an average thickness thereof was set to 0.4 µm aftercalendering. Thereby, a magnetic tape was obtained.

Calendering Process

Calendering was performed to smooth the surface of the magnetic layer.At this time, the temperature of the calendering was set to a referencetemperature of 100° C., and the pressure of the calendering was set to areference pressure of 200 kg/cm, so that a gradient range ΔA was set to3.15 degrees, a height range ΔH was set to 8.80 nm, and the amount ofoozing of a lubricant was set to 3.5 µm².

Cutting Process

The magnetic tape obtained as described above was cut to a width of ½inches (12.65 mm). Thereby, the magnetic tape having an averagethickness of 5.2 µm was obtained.

Example 2

In the preparation process of the underlayer forming coating material,needle-like iron oxide powder having a large particle size (α—Fe₂O₃,average major axis length of 0.12 µm) was used instead of needle-likeiron oxide powder having a medium particle size (α—Fe₂O₃, average majoraxis length of 0.08 µm) to obtain a magnetic tape in the same manner asin Example 1 except that a gradient range ΔA was set to 4.50 degrees,and a height range ΔH was set to 9.50 nm.

Example 3

In the calendering process, the pressure of the calendering was changedto a pressure lower than the reference pressure of 200 kg/cm in Example1 to obtain a magnetic tape in the same manner as in Example 1 exceptthat a gradient range ΔA was set to 3.40 degrees, a height range ΔH wasset to 9.00 nm, and the amount of oozing of a lubricant was set to 6.5µm².

Example 4

In the calendering process, the pressure of the calendering was set to apressure lower than that in Example 3 to obtain a magnetic tape in thesame manner as in Example 3 except that a gradient range ΔA was set to4.00 degrees, a height range ΔH was set to 9.30 nm, and the amount ofoozing of a lubricant was set to 7.0 µm².

Example 5

In the calendering process, the pressure of the calendering was changedto a pressure higher than the reference pressure of 200 kg/cm in Example1 to obtain a magnetic tape in the same manner as in Example 1 exceptthat a gradient range ΔA was set to 2.80 degrees, a height range ΔH wasset to 8.70 nm, and the amount of oozing of a lubricant was set to 3.2µm².

Comparative Example 1

In the calendering process, the temperature of the calendering was setto a pressure lower than the reference temperature of 100° C. in Example1 to obtain a magnetic tape in the same manner as in Example 2 exceptthat a gradient range ΔA was set to 5.20 degrees, a height range ΔH wasset to 8.50 nm, and the amount of oozing of a lubricant was set to 3.6µm².

Example 6

In the preparation process of the magnetic layer forming coatingmaterial, barium ferrite magnetic powder (hexagonal plate shape, averageaspect ratio of 2.8, average particle volume of 1600 nm³) was usedinstead of barium ferrite magnetic powder (hexagonal plate shape,average aspect ratio of 3.2, average particle volume of 2500 nm³).Further, in the preparation process of the magnetic layer formingcoating material, the amount of medium particle-sized aluminum oxidepowder added was changed to 3.0 parts by mass. Thereby, a gradient rangeΔA was set to 3.08 degrees, and a height range ΔH was set to 7.46 nm. Amagnetic tape was obtained in the same manner as in Example 1 except forthe above.

Example 7

In the calendering process, the temperature of the calendering waschanged to a temperature lower than the reference temperature of 100° C.in Example 1 (specifically, a temperature between the calenderingtemperature in Example 1 and the calendering temperature in ComparativeExample 1) to obtain a magnetic tape in the same manner as in Example 6except that a gradient range ΔA was set to 3.52 degrees, a height rangeΔH was set to 8.42 nm, and the amount of oozing of a lubricant was setto 3.6 µm².

Example 8

In the preparation process of the underlayer forming coating material,needle-like iron oxide powder having a large particle size (α—Fe₂O₃,average major axis length of 0.12 µm) was used instead of needle-likeiron oxide powder having a medium particle size (αFe₂O₃, average majoraxis length of 0.08 µm) to obtain a magnetic tape in the same manner asin Example 6 except that a gradient range ΔA was set to 4.80 degrees,and a height range ΔH was set to 6.50 nm.

Example 9

In the calendering process, the pressure of the calendering was changedto a pressure lower than the reference pressure of 200 kg/cm in Example1 to obtain a magnetic tape in the same manner as in Example 6 exceptthat a gradient range ΔA was set to 3.70 degrees, a height range ΔH wasset to 7.10 nm, and the amount of oozing of a lubricant was set to 6.4µm².

Example 10

In the calendering process, the pressure of the calendering was set to apressure lower than that in Example 9 to obtain a magnetic tape in thesame manner as in Example 9 except that a gradient range ΔA was set to4.13 degrees, a height range ΔH was set to 7.62 nm, and the amount ofoozing of a lubricant was set to 6.8 µm².

Example 11

In the calendering process, the pressure of the calendering was changedto a pressure higher than the reference pressure of 200 kg/cm in Example1 to obtain a magnetic tape in the same manner as in Example 6 exceptthat a gradient range ΔA was set to 3.10 degrees, a height range ΔH wasset to 6.90 nm, and the amount of oozing of a lubricant was set to 3.0µm².

Comparative Example 2

In the calendering process, the temperature of the calendering was setto a pressure higher than the reference temperature of 100° C. inExample 1 to obtain a magnetic tape in the same manner as in Example 6except that a gradient range ΔA was set to 2.40 degrees, a height rangeΔH was set to 6.50 nm, and the amount of oozing of a lubricant was setto 3.3 µm².

Example 12

In the preparation process of the magnetic layer forming coatingmaterial, aluminum oxide powder (α—Al₂O₃, average particle size (D50) of0.05 µm) having a small particle size was used instead of aluminum oxidepowder (α—Al₂O₃, average particle size (D50) of 0.09 µm) having a mediumparticle size to obtain a magnetic tape in the same manner as in Example6 except that a gradient range ΔA was set to 2.80 degrees, and a heightrange ΔH was set to 5.00 nm.

Example 13

In the preparation process of the underlayer forming coating material,needle-like iron oxide powder having a large particle size (α—Fe₂O₃,average major axis length of 0.12 µm) was used instead of needle-likeiron oxide powder having a medium particle size (α—Fe₂O₃, average majoraxis length of 0.08 µm) to obtain a magnetic tape in the same manner asin Example 12 except that a gradient range ΔA was set to 4.38 degrees,and a height range ΔH was set to 5.07 nm.

Comparative Example 3

In the preparation process of the magnetic layer forming coatingmaterial, the amount of small particle-sized aluminum oxide powder addedwas changed to 1.0 parts by mass. Further, in the calendering process,the temperature of the calendering was changed to a temperature lowerthan the reference temperature of 100° C. in Example 1 (specifically, atemperature between the calendering temperature in Example 1 and thecalendering temperature in Comparative Example 1).Thereby, a gradientrange ΔA was set to 3.80 degrees, a height range ΔH was set to 3.60 nm,and the amount of oozing of a lubricant was set to 3.6 µm². A magnetictape was obtained in the same manner as in Example 12 except for theabove.

Comparative Example 4

In the preparation process of the magnetic layer forming coatingmaterial, barium ferrite magnetic powder (hexagonal plate shape, averageaspect ratio of 3.2, average particle volume of 3500 nm³) was usedinstead of barium ferrite magnetic powder (hexagonal plate shape,average aspect ratio of 3.2, average particle volume of 2500 nm³).Further, in the preparation process of the magnetic layer formingcoating material, the amount of aluminum oxide powder added was changedto 10.0 parts by mass. Thereby, a gradient range ΔA was set to 3.26degrees, and a height range ΔH was set to 11.20 nm. A magnetic tape wasobtained in the same manner as in Example 1 except for the above.

Comparative Example 5

In the calendering process, the temperature of the calendering waschanged to a temperature lower than the reference temperature of 100° C.in Example 1 (specifically, a temperature between the calenderingtemperature in Example 1 and the calendering temperature in ComparativeExample 1) to obtain a magnetic tape in the same manner as inComparative Example 4 except that a gradient range ΔA was set to 4.07degrees, a height range ΔH was set to 10.20 nm, and the amount of oozingof a lubricant was set to 3.6 µm².

Evaluation SNR

SNR of a magnetic tape on which a servo pattern was written wasevaluated as follows. SNR (electromagnetic conversion characteristics)of the magnetic tape in a 25° C. environment was measured using a ½ inchtape running device (MTS Transport manufactured by Mountain EngineeringII) equipped with a recording/reproducing head and arecording/reproducing amplifier. A ring head with a gap length of 0.2 µmwas used for the recording head, and a GMR head with a distance of 0.1µm between shields was used for the reproducing head. A relative speedwas set to 6 m/s, a recording clock frequency was set to 160 MHz, and arecording track width was set to 2.0 µm. In addition, SNR was calculatedbased on the method described in the following literature. The resultswere shown in Table 1 as relative values with SNR in Comparative Example4 as 0 dB. Y. Okazaki: “An Error Rate Emulation System.”, IEEE Trans.Man., 31, pp. 3093-3095 (1995)

Friction Coefficient Ratio, Relative Friction

First, after the magnetic tape obtained as described above wasdemagnetized, five servo bands were formed by writing a servo pattern onthe magnetic tape using a servo writer. The servo pattern was made tocomply with the LTO-8 standard.

Next, a friction coefficient ratio (µ_(B)/µ_(A)) of the magnetic tapewas evaluated by the evaluation method described in the above-describedembodiment. In addition, a ratio of dynamic friction coefficients µ_(A)in Examples 1 to 13 and Comparative Examples 2 to 5 with respect to adynamic friction coefficient µ_(A) in Comparative Example 1 was obtainedusing a dynamic friction coefficient (a dynamic friction coefficientbefore full-scale recording/full-scale reproduction is performed) µ_(A)measured during the evaluation of a friction coefficient ratio, and theratio was set to be a relative friction. A specific calculation formulafor a relative friction is as follows. Relative friction = (Dynamicfriction coefficients µ_(A) in Examples 1 to 13 and Comparative Examples2 to 5)/(Dynamic friction coefficient µ_(A) in Comparative Example 1)

Table 1 shows Configurations and evaluation results of magnetic tapes inExamples 1 to 13 and Comparative Examples 1 to 5.

Table 1 Magnetic layer Underlayer Process AFM surface profile LubricantEvaluation result Magnetic powder Additive Additive Non-magnetic powderCalender ΔA [degree] ΔH [nm] Amount of oozing [µm²] SNR[clB] Relativefriction Friction coefficient ratio (µ_(B)/µ_(A)) Average particlevolume [nm³] Amount of addition [parts by mass] Average particle size[µm] Average major axis length [µm] Temperature Pressure Comparativeexample 4 3500 10.0 0.09 0.08 Reference temperature Reference pressure3.26 11.20 3.5 0.0 1.00 1.2 Comparative example 5 3500 10.0 0.09 0.08Low temperature Reference pressure 4.07 10.20 3.6 -0.2 0.98 1.2 Example1 2500 7.5 0.09 0.08 Reference temperature Reference pressure 3.15 8.803.5 0.5 1.00 1.2 Example 2 2500 7.5 0.09 0.12 Reference temperatureReference pressure 4.50 9.50 3.5 0.2 0.96 1.2 Example 3 2500 7.5 0.090.08 Reference temperature Low pressure 3.40 9.00 6.5 0.5 0.99 1.5Example 4 2500 7.5 0.09 0.08 Reference temperature Low pressure 4.009.30 7.0 0.2 0.99 2.0 Example 5 2500 7.5 0.09 0.08 Reference temperatureHigh pressure 2.80 8.70 3.2 0.5 1.00 1.2 Comparative example 1 2500 7.50.09 0.12 Low temperature Reference pressure 5.20 8.50 3.6 Difficulty inmeasurement due to powder falling-off 0.96 1.2 Example 6 1600 3.0 0.090.08 Reference temperature Reference pressure 3.08 7.46 3.5 1.6 1.00 1.2Example 7 1600 3.0 0.09 0.08 Low temperature Reference pressure 3.528.42 3.6 1.3 1.00 1.2 Example 8 1600 3.0 0.09 0.12 Reference temperatureReference pressure 4.80 6.50 3.5 1.2 0.96 1.2 Example 9 1600 3.0 0.090.08 Reference temperature Low pressure 3.70 7.10 6.4 1.5 0.99 1.4Example 10 1600 3.0 0.09 0.08 Reference temperature Low pressure 4.137.62 6.8 1.0 0.99 2.0 Example 11 1600 3.0 0.09 0.08 Referencetemperature High pressure 3.10 6.90 3.0 1.5 0.99 1.2 Comparative example2 1600 3.0 0.09 0.08 High temperature Reference pressure 2.40 6.50 3.31.7 1.05 1.2 Example 12 1600 3.0 0.05 0.08 Reference temperatureReference pressure 2.80 5.00 3.5 2.4 1.00 1.2 Example 13 1600 3.0 0.050.12 Reference temperature Reference pressure 4.38 5.07 3.5 2.0 0.98 1.2Comparative example 3 1600 1.0 0.05 0.08 Low temperature Referencepressure 3.80 3.60 3.6 Immeasurable due to sticking 1.02 1.2

Specific material names of additives and non-magnetic powders shown inTable 1 are as follows.

-   Additive: aluminum oxide powder (α—Al₂O₃)-   Non-magnetic powder: needle-like iron oxide powder (α—Fe₂O₃)-   Reference temperature: 100° C.-   Reference pressure: 200 kg/cm

FIG. 24 is a graph showing a relationship between height ranges ΔH andgradient ranges ΔA of the magnetic tapes in Examples 1 to 13 andComparative Examples 1 to 5.

The following can be seen from Table 1 and FIG. 24 .

When the height range ΔH is in a range of ΔH < 4.00 nm, a magnetic headsticks to a magnetic tape, and thus it becomes difficult for themagnetic tape to run. On the other hand, when the height range ΔH is ina range of 10.00 nm < ΔH, SNR (electromagnetic conversioncharacteristics) deteriorates due to a spacing loss.

When the gradient range ΔA is in a range of ΔA < 2.50 degrees, arelative friction increases, and thus running stability of the magnetictape deteriorates. On the other hand, when the gradient range ΔA is in arange of 5.00 degrees < ΔA, the gradient of a protrusion on the surfaceof a magnetic layer becomes excessively steep, and the protrusion isscraped when the magnetic tape is running, so that powder falls off.

When the height range ΔH is in a range of 4.00 ≤ ΔH ≤ 8.50 nm, SNR(electromagnetic conversion characteristics) can be further improved.

Thus, the height range ΔH is set to be in a range of 4.00 nm ≤ ΔH ≤10.00 nm, and the gradient range ΔA is set to be in a range of 2.50degrees ≤ ΔA, so that both excellent recording/reproducingcharacteristics (electromagnetic conversion characteristics) andexcellent running stability (low friction) can be achieved. In addition,the height range ΔH is set to be in a range of 4.00 nm ≤ ΔH ≤ 10.00 nm,and the gradient range ΔA is set to be in a range of 2.50 degrees ≤ ΔA ≤5.00 degrees, so that it is possible to achieve both excellentrecording/reproducing characteristics (electromagnetic conversioncharacteristics) and excellent running stability (low friction) and toprevent powder from falling off from the surface of the magnetic layerduring running.

While embodiments and modification examples of the present disclosurehave been described above in detail, the present disclosure is notlimited to the above embodiments and modification examples, and variousmodifications based on the technical idea of the present disclosure canbe made. For example, the configurations, methods, processes, shapes,materials, numerical values and the like exemplified in the aboveembodiments and modification examples are only examples, and asnecessary, different configurations, methods, processes, shapes,materials, numerical values and the like may be used. Theconfigurations, methods, processes, shapes, materials, numerical valuesand the like of the above embodiments and modification examples can becombined with each other as long as they do not deviate from the gist ofthe present disclosure.

The chemical formulas of the compounds and the like exemplified in theabove embodiments and modification examples are representative, and ageneral name of the same compound is not limited to the listed valencesand the like. In the numerical ranges stated in stages in the aboveembodiments and modification examples, the upper limit value or thelower limit value of the numerical range of a certain stage may bereplaced with the upper limit value or the lower limit value in thenumerical range of another stage. Unless otherwise specified, thematerials exemplified in the above embodiments and modification examplesmay be used alone or two or more thereof may be used in combination.

In addition, the present disclosure can also adopt the followingconfigurations.

-   (1) A magnetic recording medium with a tape shape including:    -   a substrate;    -   an underlayer provided on the substrate; and    -   a magnetic layer provided on the underlayer,    -   wherein the magnetic layer has a surface having an uneven shape,    -   a height range ΔH obtained from statistical information of a        height of the uneven shape is in a range of 4.00 nm ≤ ΔH ≤ 10.00        nm, and    -   a gradient range ΔA obtained from statistical information of a        gradient of the uneven shape is in a range of 2.50 degrees ≤ ΔA.-   (2) The magnetic recording medium according to (1),    -   wherein the gradient range ΔA is in a range of 2.50 degrees ≤ ΔA        ≤ 5.00 degrees.-   (3) The magnetic recording medium according to (1) or (2),    -   wherein the height range ΔH is in a range of 4.00 nm ≤ ΔH ≤ 8.50        nm.-   (4) The magnetic recording medium according to any one of (1) to    (3),    -   wherein the underlayer and the magnetic layer contain a        lubricant, and    -   the amount S of oozing of the lubricant per unit area of 12.5 µm        × 9.3 µm on the surface of the magnetic layer in vacuum is in a        range of 3.0 µm² ≤ S ≤ 6.5 µm².-   (5) The magnetic recording medium according to (4),    -   wherein the lubricant contains fatty acids and fatty acid        esters.-   (6) The magnetic recording medium according to any one of (1) to    (5),    -   wherein a friction coefficient ratio (µ_(B)/µ_(A)) between a        dynamic friction coefficient µ_(B) obtained after full-scale        recording/full-scale reproduction is performed twice and a        dynamic friction coefficient µ_(A) before the full-scale        recording/full-scale reproduction is performed is less than 2.0.-   (7) The magnetic recording medium according to any one of (1) to    (6), wherein a squareness ratio of the magnetic layer in a vertical    direction of the magnetic recording medium is 65% or more.-   (8) The magnetic recording medium according to any one of (1) to    (7), wherein an average thickness of the magnetic recording medium    is 5.3 µm or less.-   (9) The magnetic recording medium according to any one of (1) to    (8), wherein an average thickness of the magnetic layer is 80 nm or    less.-   (10) The magnetic recording medium according to any one of (1) to    (9), wherein an average thickness of the substrate is 4.4 µm or    less.-   (11) The magnetic recording medium according to any one of (1) to    (10), wherein the magnetic layer contains a magnetic powder, and the    average particle volume of the magnetic powder is 2500 nm³ or less.-   (12) The magnetic recording medium according to (11), wherein the    average particle volume of the magnetic powder is 1600 nm³ or less.-   (13) The magnetic recording medium according to any one of (1) to    (10), wherein the magnetic layer contains a magnetic powder, and the    magnetic powder contains hexagonal ferrite, ε-iron oxide, or    Co-containing spinel ferrite.-   (14) The magnetic recording medium according to any one of (1) to    (13), wherein the magnetic layer includes five or more servo bands.-   (15) The magnetic recording medium according to (14), wherein the    magnetic layer includes nine or more servo bands.-   (16) The magnetic recording medium according to (14), wherein a    ratio of a total area of the five or more servo bands with respect    to an area of the surface of the magnetic layer is 4.0% or less.-   (17) The magnetic recording medium according to any one of (14) to    (16), wherein a width of the servo band is 95 µm or less.-   (18) The magnetic recording medium according to any one of (1) to    (17), wherein the magnetic layer is configured to be able to form a    plurality of data tracks, and    -   a width of the data track is 2000 nm or less.-   (19) The magnetic recording medium according to any one of (1) to    (18), wherein the substrate contains polyester.-   (20) A cartridge comprising the magnetic recording medium according    to any one of (1) to (19).

REFERENCE SIGNS LIST

-   10 Cartridge-   11 Cartridge memory-   31 Antenna coil-   32 Rectification and power circuit-   33 Clock circuit-   34 Detection and modulation circuit-   35 Controller-   36 Memory-   36A First storage region-   36B Second storage region-   41 Substrate-   42 Underlayer-   43 Magnetic layer-   44 Back layer-   110 Servo frame-   111 Servo subframe 1-   111A A burst-   111B B burst-   112 Servo subframe 2-   112C C burst-   112C C burst-   113 Servo stripe-   MT Magnetic tape-   SB Servo band-   DB Data bind

1. A magnetic recording medium with a tape shape comprising: asubstrate; an underlayer provided on the substrate; and a magnetic layerprovided on the underlayer, wherein the magnetic layer has a surfacehaving an uneven shape, a height range ΔH obtained from statisticalinformation of a height of the uneven shape is in a range of 4.00 nm ≤ΔH ≤ 10.00 nm, and a gradient range ΔA obtained from statisticalinformation of a gradient of the uneven shape is in a range of 2.50degrees ≤ ΔA.
 2. The magnetic recording medium according to claim 1,wherein the gradient range ΔA is in a range of 2.50 degrees ≤ ΔA ≤ 5.00degrees.
 3. The magnetic recording medium according to claim 1, whereinthe height range ΔH is in a range of 4.00 nm ≤ ΔH < 8.50 nm.
 4. Themagnetic recording medium according to claim 1, wherein the underlayerand the magnetic layer contain a lubricant, and the amount S of oozingof the lubricant per unit area of 12.5 µm × 9.3 µm on the surface of themagnetic layer in vacuum is in a range of 3.0 µm² ≤ S ≤ 6.5 µm².
 5. Themagnetic recording medium according to claim 4, wherein the lubricantcontains fatty acids and fatty acid esters.
 6. The magnetic recordingmedium according to claim 1, wherein a friction coefficient ratio(µ_(B)/µ_(A)) between a dynamic friction coefficient µ_(B) obtainedafter full-scale recording/full-scale reproduction is performed twiceand a dynamic friction coefficient µ_(A) before the full-scalerecording/full-scale reproduction is performed is less than 2.0.
 7. Themagnetic recording medium according to claim 1, wherein a squarenessratio of the magnetic layer in a vertical direction of the magneticrecording medium is 65% or more.
 8. The magnetic recording mediumaccording to claim 1, wherein an average thickness of the magneticrecording medium is 5.3 µm or less.
 9. The magnetic recording mediumaccording to claim 1, wherein an average thickness of the magnetic layeris 80 nm or less.
 10. The magnetic recording medium according to claim1, wherein an average thickness of the substrate is 4.4 µm or less. 11.The magnetic recording medium according to claim 1, wherein the magneticlayer contains a magnetic powder, and the average particle volume of themagnetic powder is 2500 nm³ or less.
 12. The magnetic recording mediumaccording to claim 11, wherein the average particle volume of themagnetic powder is 1600 nm³ or less.
 13. The magnetic recording mediumaccording to claim 1, wherein the magnetic layer contains a magneticpowder, and the magnetic powder contains hexagonal ferrite, ε-ironoxide, or Co -containing spinel ferrite.
 14. The magnetic recordingmedium according to claim 1, wherein the magnetic layer includes five ormore servo bands.
 15. The magnetic recording medium according to claim14, wherein the magnetic layer includes nine or more servo bands. 16.The magnetic recording medium according to claim 14, wherein a ratio ofa total area of the five or more servo bands with respect to an area ofthe surface of the magnetic layer is 4.0% or less.
 17. The magneticrecording medium according to claim 14, wherein a width of the servoband is 95 µm or less.
 18. The magnetic recording medium according toclaim 1, wherein the magnetic layer is configured to be able to form aplurality of data tracks, and a width of the data track is 2000 nm orless.
 19. The magnetic recording medium according to claim 1, whereinthe substrate contains polyester.
 20. A cartridge comprising themagnetic recording medium according to claim 1.